Magnetic recording medium

ABSTRACT

A magnetic recording medium is provided and includes a magnetic layer, a non-magnetic layer, a base layer and a back layer, wherein an average thickness tT of the magnetic recording medium is tT≤5.3 μm, a dimensional change amount Δw in a width direction with respect to a change in tension in a longitudinal direction is 700 ppm/N≤Δw, a thickness of the non-magnetic layer is 2.0 μm or less, a squareness ratio measured in a vertical direction of the magnetic recording medium is 65% or more, and the magnetic layer includes a magnetic powder.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/510,024, filed on Jul. 12, 2019, which application claims the benefitof Japanese Priority Patent Application JP 2019-086720 filed on Apr. 26,2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present technology relates to a magnetic recording medium.

BACKGROUND ART

In recent years, in magnetic tapes (magnetic recording mediums) used asdata storage for computers, a track width and a distance betweenadjacent tracks have become very narrow in order to improve a recordingdensity of data. Thus, when the track width and the distance between thetracks are narrow as described above, a maximum allowable change amountas a dimensional change amount of a tape itself due to environmentalfactors such as, for example, a change or the like in temperature andhumidity becomes small.

Several technologies for reducing the dimensional change amount havebeen proposed so far. For example, in the magnetic tape medium disclosedin PTL 1 below, in a case where a Young's modulus of a nonmagneticsupport in a width direction is X and a Young's modulus of a back layerin the width direction is Y, X×Y is 6×10⁵ or more if X is 850 kg/mm² orgreater or less than 850 kg/mm² and Y/Z is 6.0 or less when a Young'smodulus of a layer in the width direction including a magnetic layer isZ.

CITATION LIST Patent Literature

[PTL 1]

JP 2005-332510A

SUMMARY Technical Problem

It is desirable to provide a magnetic recording medium capable ofsuppressing a dimensional change in a width direction by adjustingtension applied in a longitudinal direction of a tape.

Solution to Problem

According to an embodiment of the present technology, there is provideda magnetic recording medium of which

an average thickness t_(T) is t_(T)≤5.6 μm,

a dimensional change amount Δw in a width direction with respect to achange in tension in a longitudinal direction is 660 ppm/N≤Δw,

a squareness ratio in a vertical direction is 65% or more, and

a width deformation coefficient b during long-term storage in a casewhere a long-term storage width change amount Y is defined as Y=blog(t)is −0.06 μm≤b≤0.06 μm.

The magnetic recording medium may be used in a timing servo typemagnetic recording and reproducing apparatus.

The dimensional change amount Δw may be 700 ppm/N≤Δw.

The dimensional change amount Δw may be 750 ppm/N≤Δw.

The dimensional change amount Δw may be 800 ppm/N≤Δw.

The magnetic recording medium may include the back layer, and a surfaceroughness R_(ab) of the back layer may be 3.0 nm≤R_(ab)≤7.5 nm.

The magnetic recording medium may include a magnetic layer and a backlayer, and a friction coefficient μ between a surface on a side of themagnetic layer, and a surface on a side of the back layer may be0.20≤μ≤0.80.

A thermal expansion coefficient α of the magnetic recording medium maybe 5.5 ppm/° C.≤α≤9 ppm/° C., and a humidity expansion coefficient β ofthe magnetic recording medium may be β≤5.5 ppm/% RH.

A Poisson's ratio ρ of the magnetic recording medium may be 0.25≤ρ.

An elastic limit value σ_(MD) of the magnetic recording medium in thelongitudinal direction may be 0.7 N≤σ_(MD).

The elastic limit value σ_(MD) may not depend on a speed V at a time ofmeasuring an elastic limit.

The magnetic recording medium may include a magnetic layer, and themagnetic layer may be vertically aligned.

The magnetic recording medium may include the back layer and an averagethickness t_(b) of the back layer may be t_(b)≤0.6 μm.

According to another embodiment of the present technology, the magneticrecording medium may include a magnetic layer, and the magnetic layermay be a sputtered layer.

In a case where the magnetic layer is a sputtered layer, an averagethickness t_(m) of the magnetic layer may be 9 nm≤t_(m)≤90 nm.

According to still another embodiment of the present technology, themagnetic recording medium may include a magnetic layer, and the magneticlayer may contain magnetic powder.

In a case where the magnetic layer contains magnetic powder, the averagethickness t_(m) of the magnetic layer may be 35 nm≤t_(m)≤90 nm.

The magnetic powder may contain ε iron oxide magnetic powder, bariumferrite magnetic powder, cobalt ferrite magnetic powder, or strontiumferrite magnetic powder.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing a configuration of a magneticrecording medium according to a first embodiment.

FIG. 2 is a cross-sectional view showing a configuration of a magneticparticle.

FIG. 3A is a perspective view showing a configuration of a measurementdevice.

FIG. 3B is a schematic view showing the details of a measurement device.

FIG. 4 is a graph showing an example of an SFD curve.

FIG. 5 is a schematic view showing a configuration of a recording andreproducing apparatus.

FIG. 6 is a cross-sectional view showing a configuration of a magneticparticle in a modification.

FIG. 7 is a cross-sectional view showing a configuration of a magneticrecording medium in a modification.

FIG. 8 is a cross-sectional view showing a configuration of a magneticrecording medium according to a second embodiment.

FIG. 9 is a schematic view showing a configuration of a sputteringapparatus.

FIG. 10 is a cross-sectional view showing a configuration of a magneticrecording medium according to a third embodiment.

FIGS. 11A to 11C are a schematic view showing a method of measuring aservo track width.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments for implementing the presenttechnology will be described.

Note that the embodiments described below show representativeembodiments of the present technology, and the scope of the presenttechnology is not limited to only these embodiments.

The present technology will be described in the following order.

1. Description of the present technology

2. First embodiment (example of coating type magnetic recording medium)

(1) Configuration of magnetic recording medium

(2) Description of each layer

(3) Physical properties and structure

(4) Method of manufacturing magnetic recording medium

(5) Recording and reproducing apparatus

(6) Effect

(7) Modification

3. Second embodiment (example of vacuum thin film type magneticrecording medium)

(1) Configuration of magnetic recording medium

(2) Description of each layer

(3) Physical properties and structure

(4) Configuration of sputtering apparatus

(5) Method of manufacturing magnetic recording medium

(6) Effect

(7) Modification

4. Third embodiment (example of vacuum thin film type magnetic recordingmedium)

5. Example

1. DESCRIPTION OF THE PRESENT TECHNOLOGY

There is a need to further increase a recording capacity per magneticrecording cartridge. For example, in order to increase the recordingcapacity, it is conceivable to increase a tape length per magneticrecording cartridge by reducing a thickness of a magnetic recordingmedium (e.g., a magnetic recording tape) included in the magneticrecording cartridge (reducing an overall thickness).

However, as the magnetic recording medium becomes thinner, a dimensionalchange may occur in a track width direction. The dimensional change isparticularly likely to occur in a case where the magnetic recordingmedium is stored for a long time. The dimensional change in the widthdirection may cause an undesirable phenomenon for magnetic recording,such as, for example, an off-track phenomenon, etc. The off-trackphenomenon refers to a situation in which a target track is not presentat a track position for a magnetic head to read or a situation in whichthe magnetic head reads a wrong track position.

In the past, in order to suppress the dimensional change of the magneticrecording medium, for example, a method of adding a layer forsuppressing the dimensional change of the magnetic recording medium orthe like is performed.

However, the addition of the layer may increase a thickness of themagnetic recording tape and does not increase a tape length percartridge product.

The inventors of the present technology are examining a magneticrecording medium suitable for use in a recording and reproducingapparatus, whose width may be kept constant or substantially constant byadjusting tension of the long-shaped magnetic recording medium in alongitudinal direction. The recording and reproducing apparatus detects,for example, dimensions or a dimensional change in the width directionof the magnetic recording medium, and adjusts tension in thelongitudinal direction on the basis of a detection result.

However, in the magnetic recording medium suppressed in the dimensionalchange, the dimensional change amount in the width direction based onthe change in tension in the longitudinal direction is small. Therefore,it is difficult to keep the width of the magnetic recording mediumconstant or substantially constant even though tension is adjusted inthe longitudinal direction by the recording and reproducing apparatus.

In consideration of the above circumstances, the present inventorsexamined a magnetic recording medium which is thin and suitable for usein a recording and reproducing apparatus that adjusts tension in alongitudinal direction and which suppresses deterioration of suitabilityfor use in the recording and reproducing apparatus due to storage. As aresult, the present inventors have found that a magnetic recordingmedium having a specific configuration satisfies these requirements. Inother words, the present technology provides a magnetic recording mediumof which an average thickness t_(T) is t_(T)≤5.6 μm, a dimensionalchange amount Δw in a width direction with respect to a change intension in a longitudinal direction is 660 ppm/N≤Δw, a squareness ratioin a vertical direction is 65% or more, and a width deformationcoefficient b during long-term storage in a case where a long-termstorage width change amount Y is defined as Y=blog(t) is −0.06≤b≤0.06.

The average thickness t_(T) of the magnetic recording medium accordingto the embodiment of the present technology is 5.6 μm or less, morepreferably 5.5 μm or less, and still more preferably 5.3 μm or less, 5.2μm or less, 5.0 μm or less, or 4.6 μm or less. Because the magneticrecording medium is so thin, for example, the length of the tape woundup in one magnetic recording cartridge can be longer, thereby increasinga recording capacity per magnetic recording cartridge.

In the magnetic recording medium according to the embodiment of thepresent technology, the dimensional change amount Δw in the widthdirection with respect to the change in tension in the longitudinaldirection is 660 ppm/N or more, more preferably 670 ppm/N or more, andstill more preferably 700 ppm/N or more, 710 ppm/N or more, 730 ppm/N ormore, 750 ppm/N or more, 780 ppm/N or more, or 800 ppm/N or more. Thefact that the magnetic recording medium has the dimensional changeamount Δw within the above numerical range contributes to making itpossible to maintain the width of the magnetic recording medium at aconstant level by adjusting tension of the magnetic recording medium inthe longitudinal direction.

Furthermore, an upper limit of the dimensional change amount Δw is notparticularly limited, and may be, for example, 1700000 ppm/N or less,preferably 20000 ppm/N or less, more preferably 8000 ppm/N or less,still more preferably 5000 ppm/N or less, 4000 ppm/N or less, 3000 ppm/Nor less, or 2000 ppm/N or less. In a case where the dimensional changeamount Δw is too large, it may be difficult to stably run in themanufacturing process.

A method of measuring the dimensional change amount Δw will be describedin (3) of 2. below.

The magnetic recording medium according to the embodiment of the presenttechnology may have a squareness ratio S2 in the vertical direction of65% or more, preferably 73% or more, and more preferably 80% or more.Because the magnetic recording medium has a squareness ratio S2 withinthe above numerical range, more excellent electromagnetic conversioncharacteristic may be obtained. Furthermore, a servo signal shape isimproved, making it easier to control a drive side.

A method of measuring a squareness ratio S2 in the vertical directionwill be described in (3) of 2. below.

As described above, the magnetic recording medium according to theembodiment of the present technology is thin, suitable for a recordingand reproducing apparatus that adjusts tension in the longitudinaldirection, and is excellent in electromagnetic conversioncharacteristic, and thus, a recording capacity per magnetic recordingcartridge may be significantly increased.

Moreover, in the magnetic recording medium according to the embodimentof the present technology, a width deformation coefficient b duringlong-term storage in a case where a long-term storage width changeamount Y is defined as Y=blog(t) may be −0.06 μm or more, preferably−0.05 μm, and more preferably −0.04 μm or more. Furthermore, the widthdeformation coefficient b may be 0.06 μm or less, preferably 0.05 μm orless, and more preferably 0.04 μm or less. When the width deformationcoefficient b of the magnetic recording medium is within the abovenumerical range, the suitability for use in the recording andreproducing apparatus does not change even in a case where the magneticrecording medium is stored for a long period of time. Therefore, forexample, a phenomenon undesirable for magnetic recording, such as anoff-track phenomenon, does not easily occur.

A method of calculating the width deformation coefficient b will bedescribed in (3) of 2. below. The magnetic recording medium according tothe embodiment of the present technology preferably includes a backlayer, and a surface roughness R_(ab) of the back layer is preferably3.0 nm≤R_(ab)≤7.5 nm, and more preferably 3.0 nm≤R_(ab)≤7.3 nm. Thesurface roughness R_(ab) within the above numerical range contributes toimprovement of handling properties of the magnetic recording medium.

The surface roughness R_(ab) of the back layer is more preferably 7.2 nmor less, and still more preferably 7.0 nm or less, 6.5 nm or less, 6.3nm or less, or 6.0 nm or less. Furthermore, the surface roughness R_(ab)may be more preferably 3.2 nm or more, and still more preferably 3.4 nmor more. When the surface roughness R_(ab) of the back layer is in theabove-mentioned numerical range, in particular, being theabove-mentioned upper limit value or less, good electromagneticconversion characteristic can be achieved in addition to the improvementof the handling properties.

A method of measuring the surface roughness R_(ab) will be described in(3) of 2. below.

The magnetic recording medium according to the embodiment of the presenttechnology is preferably a long (or elongated) magnetic recordingmedium, and may be, for example, a magnetic recording tape (inparticular, a long magnetic recording tape).

A magnetic recording medium according to the embodiment of the presenttechnology may include a magnetic layer, a base layer, and a back layer,and may include any other layer in addition to those layers. The otherlayer may be appropriately selected according to types of magneticrecording medium. The magnetic recording medium may be, for example, acoating type magnetic recording medium or a vacuum thin film typemagnetic recording medium. The coating type magnetic recording mediumwill be described in more detail in 2. below. The vacuum thin film typemagnetic recording medium will be described in more detail in 3. and 4.below. For the layers included in the magnetic recording medium otherthan the above three layers, those descriptions may be referred to.

The magnetic recording medium according to the embodiment of the presenttechnology may have, for example, at least one data band and at leasttwo servo bands. The number of the data bands may be, for example, 2 to10, particularly, 3 to 6, and more particularly, 4 or 5. The number ofthe servo bands may be, for example, 3 to 11, particularly, 4 to 7, andmore particularly, 5 or 6. These servo bands and data bands may bearranged, for example, to extend in the longitudinal direction of thelong-shaped magnetic recording medium (in particular, a magneticrecording tape), and in particular, to be substantially parallel. Thedata bands and the servo bands may be provided in the magnetic layer.The magnetic recording media having the data bands and the servo bandsmay include a magnetic recording tape conforming to the linear tape-open(LTO) standard. In other words, the magnetic recording medium may be amagnetic recording tape conforming to the LTO standard. For example, themagnetic recording medium may be a magnetic recording tape conforming toLTO8 or a later standard (e.g., LTO9, LTO10, LTO11, LTO12, etc.).

A width of the long-shaped magnetic recording medium (particularly,magnetic recording tape) may be, for example, 5 mm to 30 mm,particularly, 7 mm to 25 mm, more particularly, 10 mm to 20 mm, and evenmore particularly, 11 mm to 19 mm. The length of the long-shapedmagnetic recording medium (in particular, the magnetic recording tape)may be, for example, 500 m to 1,500 m. For example, a tape widthaccording to the LTO8 standard is 12.65 mm and a length is 960 m.

2. FIRST EMBODIMENT (EXAMPLE OF COATING TYPE MAGNETIC RECORDING MEDIUM)

(1) Configuration of Magnetic Recording Medium

First, a configuration of a magnetic recording medium 10 according to afirst embodiment will be described with reference to FIG. 1. Themagnetic recording medium 10 is, for example, a magnetic recordingmedium subjected to vertical alignment processing, and includes along-shaped base layer (also referred to as substrate) 11, a groundlayer (non-magnetic layer) 12 provided on one principal plane of thebase layer 11, a magnetic layer (also referred to as a record layer) 13provided on the ground layer 12, and a back layer 14 provided on theother principal plane of the base layer 11 as shown in FIG. 1.Hereinafter, among the both principal planes of the magnetic recordingmedium 10, the plane on which the magnetic layer 13 is provided will bereferred to as a magnetic surface, and the plane opposite to themagnetic surface (the plane on which the back layer 14 is provided) willbe referred to as a back surface.

The magnetic recording medium 10 has a long shape and runs in thelongitudinal direction during recording and reproducing. Furthermore,the magnetic recording medium 10 may be configured to be able to recorda signal at a shortest recording wavelength of preferably 100 nm orless, more preferably 75 nm or less, still more preferably 60 nm orless, particularly preferably 50 nm or less, and may be used for, forexample, a recording and reproducing apparatus whose shortest recordingwavelength is in the above range. The recording and reproducingapparatus may include a ring type head as a recording head. A recordingtrack width is, for example, 2 μm or less.

(2) Description of Each Layer

(Base Layer)

The base layer 11 may function as a support of the magnetic recordingmedium 10, and may be, for example, a long-shaped flexible non-magneticsubstrate, and in particular, may be a non-magnetic film. A thickness ofthe base layer 11 may be, for example, 2 μm to 8 preferably 2.2 μm to 7more preferably 2.5 μm to 6 and still more preferably 2.6 μm to 5 μm.The base layer 11 may contain, for example, at least one of apolyester-based resin, a polyolefin-based resin, a cellulose derivative,a vinyl-based resin, an aromatic polyether ketone resin, or any otherpolymer resin. In a case where the base layer 11 contains two or more ofthe above-described materials, the two or more materials may be mixed,copolymerized, or stacked.

Examples of the polyester-based resin may include one or a mixture oftwo or more of polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polybutylene terephthalate (PBT), polybutylenenaphthalate (PBN), polycyclohexylene dimethylene terephthalate (PCT),polyethylene-p-oxybenzoate (PEB), and polyethylenebisphenoxycarboxylate.According to a preferred embodiment of the present technology, the baselayer 11 may include PET or PEN.

The polyolefin-based resin may be, for example, one or a mixture of twoor more of polyethylene (PE) and polypropylene (PP).

The cellulose derivative may be, for example, one or a mixture of two ormore of cellulose diacetate, cellulose triacetate, cellulose acetatebutyrate (CAB), and cellulose acetate propionate (CAP).

The vinyl-based resin may be, for example, one or a mixture of two ormore of polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC).

The aromatic polyether ketone resin may be, for example, one or amixture of two or more of polyether ketone (PEK), polyether ether ketone(PEEK), polyether ketone ketone (PEKK), and polyether ether ketoneketone (PEEKK). According to a preferred embodiment of the presenttechnology, the base layer 11 may include PEEK.

Examples of any other polymer resin may be, for example, one or amixture of two or more of polyamide (PA, nylon), aromatic PA (aromaticpolyamide, aramid), polyimide (PI), aromatic PI, polyamide imide (PAI),aromatic PAI, polybenzoxazole (PBO) (e.g., Zylon (registeredtrademark)), polyether, polyether ester, polyether sulfone (PES),polyether imide (PEI), polysulfone (PSF), polyphenylene sulfide (PPS),polycarbonate (PC), polyarylate (PAR), and polyurethane (PU).

(Magnetic Layer)

The magnetic layer 13 may be, for example, a perpendicular record layer.The magnetic layer 13 may contain magnetic powder. The magnetic layer 13may further contain, for example, a binder and conductive particles inaddition to the magnetic powder. The magnetic layer 13 may furthercontain, for example, additives such as a lubricant, an abrasive, acorrosion inhibitor, and the like, as necessary.

An average thickness t_(m) of the magnetic layer 13 is preferably 35nm≤t_(m)≤120 nm, more preferably 35 nm≤t_(m)≤100 nm, and particularlypreferably 35 nm≤t_(m)≤90 nm. When the average thickness t_(m) of themagnetic layer 13 is within the above numerical range, the magneticlayer 13 contributes to improvement of electromagnetic conversioncharacteristic.

The average thickness t_(m) of the magnetic layer 13 may be obtained asfollows. First, a specimen is fabricated by processing the magneticrecording medium 10 perpendicularly to a main surface thereof, and across-section of the specimen is observed by a transmission electronmicroscope (TEM) under the following conditions.

Device: TEM (H9000NAR manufactured by Hitachi, Ltd.)

Acceleration voltage: 300 kV

Magnification: 100,000 times

Next, using an obtained TEM image, a thickness of the magnetic layer 13is measured at positions of at least 10 spots in the longitudinaldirection of the magnetic recording medium 10, and thereafter, themeasured values are simply averaged (arithmetic mean) to be determinedas an average thickness t_(m) (nm) of the magnetic layer 13.

The magnetic layer 13 is preferably a vertically aligned magnetic layer.In the present specification, vertical alignment refers to that asquareness ratio S1 measured in the longitudinal direction (runningdirection) of the magnetic recording medium 10 is 35% or less. A methodof measuring the squareness ratio S1 will be described separately below.

Note that the magnetic layer 13 may be a magnetic layer which isin-plane aligned (longitudinal alignment). In other words, the magneticrecording medium 10 may be a horizontal recording type magneticrecording medium. However, vertical alignment is more preferable interms of higher recording density.

(Magnetic Powder)

Examples of magnetic particles forming magnetic powder contained in themagnetic layer 13 may contain epsilon type iron oxide (6 iron oxide),gamma hematite, magnetite, chromium dioxide, cobalt-coated iron oxide,hexagonal ferrite, barium ferrite (BaFe), Co ferrite, strontium ferrite,a metal, or the like, but are not limited thereto. The magnetic powdermay be one or a combination or two or more thereof. In particular,preferably, the magnetic powder may contain ε iron oxide magneticpowder, barium ferrite magnetic powder, cobalt ferrite magnetic powder,or strontium ferrite magnetic powder. Note that ε iron oxide may containGa and/or Al. These magnetic particles may be appropriately selected bythose skilled in the art on the basis of factors such as, for example,the method of manufacturing the magnetic layer 13, specifications of thetape, a function of the tape, and the like.

An average particle size (average maximum particle size) D of themagnetic powder may be preferably 22 nm or less, more preferably 8 nm to22 nm, and still more preferably 10 nm to 20 nm.

The average particle size D of the above magnetic powder is obtained asfollows. First, the magnetic recording medium 10 to be measured isprocessed by a focused ion beam (FIB) method or the like to produce athin piece, and a cross-section of the thin piece is observed by atransmission electron microscope (TEM). Next, 500 ε iron oxide particlesare randomly selected from the captured TEM image, a maximum particlesize d_(max) of each particle is measured, and a particle sizedistribution of the maximum particle size d_(max) of the magnetic powderis obtained. Here, the “maximum particle size d_(max)” refers to theso-called maximum Feret diameter. Specifically, the “maximum particlesize d_(max)” refers to a maximum distance among distances between twoparallel lines drawn from all angles so as to be in contact with outlineof the ε iron oxide particle. Thereafter, a median diameter (50%diameter, D50) of the maximum particle size d_(max) is obtained from theparticle size distribution of the obtained maximum particle sized_(max), and is determined as an average particle size (average maximumparticle size) D of the magnetic powder.

A shape of the magnetic particles depends on a crystal structure of themagnetic particles. For example, BaFe and strontium ferrites may have ahexagonal plate shape. The ε iron oxide may be spherical. The cobaltferrite may be cubic. The metal may have a spindle shape. These magneticparticles are aligned in a manufacturing process of the magneticrecording medium 10. According to a preferred embodiment of the presenttechnology, the magnetic powder may contain powder of nanoparticlespreferably containing ε iron oxide (hereinafter, referred to as “ε ironoxide particles”). Even with the fine particles of ε iron oxideparticles, high coercive force can be obtained. Preferably, the ε ironoxide contained in the ε iron oxide particle is preferentiallycrystal-aligned in a thickness direction (vertical direction) of themagnetic recording medium 10.

The ε iron oxide particles have a spherical or substantially sphericalshape or have a cubic or substantially cubic shape. Since the ε ironoxide particles have the shape as mentioned above, in a case where εiron oxide particles are used as the magnetic particles, a contact areabetween particles in a thickness direction of the medium is reduced tothus suppress aggregation of the particles, as compared with a casewhere barium ferrite particles having a hexagonal plate-like shape areused as magnetic particles. Therefore, dispersibility of the magneticpowder may be increased to thus obtain a better signal-to-noise ratio(SNR).

The ε iron oxide particles have a core-shell type structure.Specifically, as shown in FIG. 2, the iron oxide particle includes acore portion 21 and a shell portion 22 provided around the core portion21 and having a two-layer structure. The shell portion 22 having thetwo-layer structure includes a first shell portion 22 a provided on thecore portion 21 and a second shell portion 22 b provided on the firstshell portion 22 a.

The core portion 21 contains ε iron oxide. The ε iron oxide contained inthe core portion 21 preferably has an ε-Fe₂O₃ crystal as a main phase,and more preferably includes a single phase ε-Fe₂O₃.

The first shell portion 22 a covers at least a portion of the peripheryof the core portion 21.

Specifically, the first shell portion 22 a may partially cover theperiphery of the core portion 21 or may cover the entire periphery ofthe core portion 21. If exchange coupling of the core portion 21 and thefirst shell portion 22 a is sufficient and in terms of improvement ofmagnetic characteristic, the first shell portion 22 a preferably coversthe entire surface of the core portion 21.

The first shell portion 22 a is a so-called soft magnetic layer, and maycontain, for example, a soft magnetic material such as α-Fe, a Ni—Fealloy, an Fe—Si—Al alloy, or the like. α-Fe may be obtained by reducingthe ε iron oxide contained in the core portion 21.

The second shell portion 22 b is an oxide film as an anti-oxidationlayer. The second shell portion 22 b may contain a iron oxide, aluminumoxide, or silicon oxide. The a iron oxide may contain, for example, atleast one of Fe₃O₄, Fe₂O₃, or FeO. In a case where the first shellportion 22 a contains α-Fe (soft magnetic material), the α-iron oxidemay be obtained by oxidizing α-Fe contained in the first shell portion22 a.

Since the ε iron oxide particles have the first shell portion 22 a asdescribed above, thermal stability may be ensured, whereby the coerciveforce Hc of the single core portion 21 may be maintained at a largevalue and/or the overall coercive force Hc of the ε iron oxide particles(core shell type particles) may be adjusted to the coercive force Hcappropriate for recording.

Furthermore, since the ε iron oxide particles have the second shellportion 22 b as described above, the ε iron oxide particles areprevented from being exposed in the air during or before themanufacturing process of the magnetic recording medium 10 to cause theparticle surfaces to be rusted, or the like, and thus, a degradation ofthe characteristic of the ε iron oxide particles can be suppressed.Therefore, a degradation of the characteristics of the magneticrecording medium 10 may be suppressed.

The ε iron oxide particle may have a shell portion 23 having a singlelayer structure as shown in FIG. 6. In this case, the shell portion 23has a configuration similar to that of the first shell portion 22 a.However, from the viewpoint of suppressing the degradation of thecharacteristics of the ε iron oxide particle, the ε iron oxide particlepreferably has the shell portion 22 having a two-layer structure.

The ε iron oxide particle may contain an additive instead of thecore-shell type structure, or may have the core-shell type structure andmay contain the additive as well. In these cases, a part of Fe of the εiron oxide particle is replaced by the additive. Since the coerciveforce Hc of the entire ε iron oxide particle may be adjusted to thecoercive force Hc suitable for recording also by the ε iron oxideparticle containing the additive, ease of recording may be improved. Theadditive is one or more selected from the group including metal elementother than iron, preferably trivalent metal element, more preferablyaluminum (Al), gallium (Ga), and indium (In).

Specifically, the ε iron oxide containing the additive is anε-Fe_(2-x)M_(x)O₃ crystal (here, M is one or more selected from thegroup including metal elements other than iron, preferably trivalentmetal elements, more preferably Al, Ga, and In) and x is, for example,0<x<1).

According to another preferred embodiment of the present technology, themagnetic powder may be barium ferrite (BaFe) magnetic powder. The bariumferrite magnetic powder contains magnetic particles of iron oxidecontaining barium ferrite as a main phase (hereinafter referred to as“barium ferrite particles”). The barium ferrite magnetic powder has highreliability of data recording, for example, in that the coercive forceis not lowered even in a high temperature and high humidity environment,and the like. From this viewpoint, barium ferrite magnetic powder ispreferable as the magnetic powder.

An average particle size of the barium ferrite magnetic powder is 50 nmor less, more preferably 10 nm to 40 nm, and still more preferably 12 nmto 25 nm.

In a case where the magnetic layer 13 contains the barium ferritemagnetic powder as magnetic powder, an average thickness t_(m) [nm] ofthe magnetic layer 13 is preferably 35 nm≤t_(m)≤100 nm. Furthermore, thecoercive force Hc of the magnetic recording medium 10 measured in athickness direction (vertical direction) is preferably 160 kA/m to 280kA/m, more preferably 165 kA/m to 275 kA/m, and still more preferably170 kA/m to 270 kA/m.

According to yet another preferred embodiment of the present technology,the magnetic powder may be cobalt ferrite magnetic powder. The cobaltferrite magnetic powder contains magnetic particles of iron oxidecontaining cobalt ferrite as a main phase (hereinafter referred to as“cobalt ferrite magnetic particles”). The cobalt ferrite magneticparticles preferably have uniaxial anisotropy. The cobalt ferritemagnetic particles have, for example, a cubic shape or a substantiallycubic shape. The cobalt ferrite is cobalt ferrite containing Co. Thecobalt ferrite may further contain one or more selected from the groupincluding Ni, Mn, Al, Cu, and Zn in addition to Co.

The cobalt ferrite has, for example, an average composition representedby the following Formula (1).

Co_(x)M_(y)Fe₂O_(z)  (1)

(where, in Formula (1), M is, for example, one or more metals selectedfrom the group including Ni, Mn, Al, Cu, and Zn; x is a value within arange of 0.4≤x≤1.0; y is a value within the range of 0≤y≤0.3; however, xand y satisfy the relationship of (x+y)≤1.0; z is a value within a rangeof 3≤z≤4; a part of Fe may be substituted by another metal element).

An average particle size of the cobalt ferrite magnetic powder ispreferably 25 nm or less, more preferably 23 nm or less. The coerciveforce Hc of the cobalt ferrite magnetic powder is preferably 2500 Oe ormore, and more preferably 2600 Oe or more and 3500 Oe or less.

According to yet another preferred embodiment of the present technology,the magnetic powder may contain powder of nanoparticles containinghexagonal ferrite (hereinafter, referred to as “hexagonal ferriteparticles”). The hexagonal ferrite particle has, for example, ahexagonal plate shape or a substantially hexagonal plate shape. Thehexagonal ferrite may preferably contain at least one of Ba, Sr, Pb orCa, and more preferably at least one of Ba or Sr. The hexagonal ferritemay be, for example, barium ferrite or strontium ferrite. The bariumferrite may further contain at least one of Sr, Pb, or Ca in addition toBa. The strontium ferrite may further contain at least one of Ba, Pb orCa in addition to Sr.

More specifically, the hexagonal ferrite may have an average compositionrepresented by a general formula MFe₁₂O₁₉. Here, M is, for example, atleast one metal of Ba, Sr, Pb, and Ca, preferably at least one metal ofBa and Sr. M may be a combination of Ba and at least one metal selectedfrom the group including Sr, Pb, and Ca. Furthermore, M may be acombination of Sr and one or more metals selected from the groupincluding Ba, Pb, and Ca. In the above general formula, part of Fe maybe substituted by another metal element.

In a case where the magnetic powder contains powder of hexagonal ferriteparticles, an average particle size of the magnetic powder is preferably50 nm or less, more preferably 10 nm to 40 nm, and still more preferably15 nm to 30 nm.

(Binder)

The binder is preferably a resin having a structure in which acrosslinking reaction is given to a polyurethane-based resin, a vinylchloride-based resin, or the like. However, the binder is not limitedthereto, and any other resins may be appropriately mixed depending onphysical properties and the like desired for the magnetic recordingmedium 10. The resin to be mixed is not particularly limited as long asit is a resin generally used in the coating type magnetic recordingmedium 10.

The binder may include, for example, polyvinyl chloride, polyvinylacetate, a vinyl chloride-vinyl acetate copolymer, a vinylchloride-vinylidene chloride copolymer, a vinyl chloride-acrylonitrilecopolymer, an acrylic acid ester-acrylonitrile copolymer, an acrylicacid ester-vinyl chloride-vinylidene chloride copolymer, an acrylic acidester-acrylonitrile copolymer, an acrylic acid ester-vinylidene chloridecopolymer, a methacrylic acid ester-vinylidene chloride copolymer amethacrylic acid ester-vinyl chloride copolymer, a methacrylic acidester-ethylene copolymer, a polyvinyl fluoride, vinylidenechloride-acrylonitrile copolymer, an acrylonitrile-butadiene copolymer,a polyamide resin, polyvinyl butyral, a cellulose derivative (celluloseacetate butyrate, cellulose diacetate, cellulose triacetate, cellulosepropionate, and nitrocellulose), a styrene-butadiene copolymer, apolyester resin, an amino resin, synthetic rubber, and the like.Furthermore, as the binder, a thermosetting resin or a reactive resinmay be used, and examples thereof include a phenol resin, an epoxyresin, a urea resin, a melamine resin, an alkyd resin, a silicone resin,a polyamine resin, an urea-formaldehyde resin, and the like.

Furthermore, polar functional groups such as, —SO₃M, —OSO₃M, —COOM,P═O(OM)₂, or the like, may be introduced into each binder describedabove in order to improve dispersibility of the magnetic powder. Here,in the formula, M is a hydrogen atom or an alkali metal such as lithium,potassium, sodium, and the like.

Moreover, examples of the polar functional group may include a sidechain type having an end group of —NR1R2 and —NR1R2R3⁺X⁻ or a main chaintype of >NR1R2⁺X⁻. Here, in the formulas, R1, R2 and R3 are a hydrogenatom or a hydrocarbon group, and X⁻ is a halogen element ion such asfluorine, chlorine, bromine, iodine, or the like, or an inorganic ororganic ion. Furthermore, the polar functional group may also include—OH, —SH, —CN, and an epoxy group.

(Additive)

The magnetic layer 13 may further contain aluminum oxide (α, β or γalumina), chromium oxide, silicon oxide, diamond, garnet, emery, boronnitride, titanium carbide, silicon carbide, titanium carbide, titaniumoxide (rutile type titanium carbide or anatase type titanium oxide), orthe like, as nonmagnetic reinforcing particles.

(Ground Layer)

The ground layer 12 is a nonmagnetic layer containing nonmagnetic powderand a binder as main components. The above description regarding thebinder contained in the magnetic layer 13 is also applied to the bindercontained in the ground layer 12. The ground layer 12 may furthercontain at least one of additives among conductive particles, alubricant, a curing agent, a rust-preventive agent, or the like, asnecessary.

An average thickness of the ground layer 12 is preferably 0.6 μm to 2.0μm, and more preferably 0.8 μm to 1.4 μm. Note that the averagethickness of the ground layer 12 is obtained in a manner similar to thatof the average thickness t_(m) of the magnetic layer 13. However, amagnification of a TEM image is appropriately adjusted according to thethickness of the ground layer 12.

(Nonmagnetic Powder)

The nonmagnetic powder contained in the ground layer 12 may include, forexample, at least one selected from inorganic particles and organicparticles. One kind of nonmagnetic powder may be used alone, or two ormore kinds of nonmagnetic powder may be used in combination. Theinorganic particles include, for example, one or a combination of two ormore selected from metal, metal oxide, metal carbonate, metal sulfate,metal nitride, metal carbide, and metal sulfide. More specifically, theinorganic particles may be, for example, one or two or more selectedfrom iron oxyhydroxide, hematite, titanium oxide, and carbon black. Ashape of the nonmagnetic powder may include, for example, various shapessuch as a needle shape, sphere shape, cubic shape, plate shape, or thelike, but is not particularly limited thereto.

(Back Layer)

The back layer 14 may contain a binder and nonmagnetic powder. The backlayer 14 may contain various additives such as a lubricant, a curingagent, an antistatic agent, and the like, as necessary. The abovedescription of the binder and the nonmagnetic powder contained in theground layer 12 is also applied to the binder and the nonmagnetic powdercontained in the back layer 14.

An average particle size of the inorganic particles contained in theback layer 14 is preferably 10 nm to 150 nm, and more preferably 15 nmto 110 nm. The average particle size of the inorganic particles isobtained in a manner similar to that of the average particle size D ofthe magnetic powder described above.

An average thickness t_(b) of the back layer 14 is preferably t_(b)≤0.6μm. Since the average thickness t_(b) of the back layer 14 is within theabove range, even in a case where the average thickness t_(T) of themagnetic recording medium 10 is t_(T)≤5.6 μm, the thicknesses of theground layer 12 and the base layer 11 may be kept thick, whereby runningstability of the magnetic recording medium 10 in the recording andreproducing apparatus may be maintained.

The average thickness to of the back layer 14 is obtained as follows.First, a ½ inch-wide magnetic recording medium 10 is prepared and cutinto a length of 250 mm to prepare a sample.

Next, thicknesses of different spots of the sample are measured at 5 ormore points using a laser hologage manufactured by Mitsutoyo Co., Ltd.,as a measurement device, and the measured values are simply averaged(arithmetic average) to obtain an average value t_(T)[μm].

Subsequently, the back layer 14 of the sample is removed with a solventsuch as methyl ethyl ketone (MEK) or diluted hydrochloric acid, andthereafter, thicknesses of different spots of the sample are measured at5 or more points using the laser hologage and the measured values aresimply averaged (arithmetic average) to obtain an average valuet_(B)[μm]. Thereafter, the average thickness t_(b)[μm] of the back layer14 is obtained by the following equation.

t _(b)[μm]=t _(T)[μm]−t _(B)[μm]

(3) Physical Properties and Structure

(Average Thickness t_(T) of Magnetic Recording Medium)

The average thickness t_(T) of the magnetic recording medium 10 ist_(T)≤5.6 μm. When the average thickness t_(T) of the magnetic recordingmedium 10 is t_(T)≤5.6 μm, a recording capacity that can be recorded inone data cartridge can be increased as compared to the related art. Alower limit value of the average thickness t_(T) of the magneticrecording medium 10 is, for example, 3.5 μm≤t_(T), but is notparticularly limited.

The average thickness t_(T) of the magnetic recording medium 10 isobtained by the method of measuring the average value t_(T) describedabove in the method of measuring the average thickness to of the backlayer 14.

(Dimensional Change Amount Δw)

The dimensional change amount Δw [ppm/N] of the magnetic recordingmedium 10 in the width direction with respect to a change in tension ofthe magnetic recording medium 10 in the longitudinal direction is 660ppm/N≤Δw, more preferably 670 ppm/N≤Δw, more preferably 700 ppm/N≤Δw,more preferably 710 ppm/N≤Δw, more preferably 730 ppm/N≤Δw, morepreferably 750 ppm/N≤Δw, still more preferably 780 ppm/N≤Δw, andparticularly preferably 800 ppm/N≤Δw. If the dimensional change amountΔw is Δw<640 ppm/N, it may be difficult to suppress a change in width inthe adjustment of longitudinal tension by the recording and reproducingapparatus. The upper limit value of the dimensional change amount Δw isnot particularly limited. For example, Δw≤1700000 ppm/N, preferablyΔw≤20000 ppm/N, more preferably Δw≤8000 ppm/N, still more preferablyΔw≤5000 ppm/N, Δw≤4000 ppm/N, Δw≤3000 ppm/N, or Δw≤2000 ppm/N.

Those skilled in the art can appropriately set the dimensional changeamount Δw. For example, the dimensional change amount Δw may be set to adesired value by selecting a thickness of the base layer 11 and/or amaterial of the base layer 11. Furthermore, the dimensional changeamount Δw may be set to a desired value, for example, by adjusting thestretching strength in the vertical and horizontal directions of thefilm constituting the base layer. For example, Δw decreases more whenthe film is stretched more strongly in the width direction, andconversely, Δw increases when the film is stretched strongly in thelongitudinal direction.

The dimensional change amount Δw is obtained as follows. First, a ½inch-wide magnetic recording medium 10 is prepared and cut into a lengthof 250 mm to prepare a sample 10S.

Next, loads are applied in order of 0.2 N, 0.6 N, and 1.0 N in thelongitudinal direction of the sample 10S, and widths of the sample 10Sat the loads of 0.2 N, 0.6 N, and 1.0 N are measured. Subsequently, thedimensional change amount Δw is determined from the following equation.

Note that the measurement in a case of applying the load of 0.6 N iscarried out to check whether an abnormality has not occurred in themeasurement (in particular, in order to check whether these threemeasurement results are linear), and the measurement results are notused in the following equation.

$\begin{matrix}{{\Delta \; {w\left\lbrack {{ppm}/N} \right\rbrack}} = {\frac{{{D\left( {0.2N} \right)}\lbrack{mm}\rbrack} - {{D\left( {1.0N} \right)}\lbrack{mm}\rbrack}}{{D\left( {0.2N} \right)}\lbrack{mm}\rbrack} \times \frac{1,000,000}{\left( {1.0\lbrack N\rbrack} \right) - \left( {0.2\lbrack N\rbrack} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

(where, D(0.2 N) and D(1.0 N) represent widths of the sample 10S when0.2 N and 1.0 N are loaded in the longitudinal direction of sample 10S,respectively).

The widths of the sample 10S when each load is applied are measured asfollows. First, a measurement device shown in FIG. 3A including adigital dimension measuring instrument LS-7000 manufactured by KeyenceCorporation is prepared as a measurement device, and the sample 10S isset in the measurement device. Specifically, one end of the long-shapedsample (magnetic recording medium) 10S is fixed by a fixing portion 231.Next, as shown in FIG. 3A, the sample 10S is placed on fivesubstantially cylindrical and rod-like support members 232. The sample10S is placed on the five support members 232 so that a back surfacethereof is in contact with the five support members 232. The fivesupport members 232 (particularly, surfaces thereof) all includestainless steel SUS304, and a surface roughness Rz (maximum height)thereof is 0.15 μm to 0.3 μm.

The arrangement of the five rod-like support members 232 will bedescribed with reference to FIG. 3B. As shown in FIG. 3B, the sample 10Sis placed on the five support members 232.

Hereinafter, the five support members 232 will be referred to as,starting from the side closest to the fixing portion 231, a “firstsupport member”, a “second support member”, a “third support member”(having a slit 232A), a “fourth support member”, and a “fifth supportmember” (closest to a weight 233). A diameter of these five supportmembers is 7 mm. A distance d₁ between the first support member and thesecond support member (in particular, a distance between the centers ofthese support members) is 20 mm. A distance d₂ between the secondsupport member and the third support member is 30 mm. A distance d₃between the third support member and the fourth support member is 30 mm.A distance d₄ between the fourth support member and the fifth supportmember is 20 mm. Furthermore, the second support member, the thirdsupport member, and the fourth support member are arranged so thatportions of the sample 10S placed between the second support member, thethird support member, and the fourth support member forms asubstantially perpendicular plane with respect to the direction ofgravity. Furthermore, the first support member and the second supportmember are arranged so that the sample 10S forms an angle of θ₁=30° withrespect to the substantially perpendicular plane between the firstsupport member and the second support member. Moreover, the fourthsupport member and the fifth support member are arranged so that thesample 10S forms an angle of θ₂=30° with respect to the substantiallyperpendicular plane between the fourth support member and the fifthsupport member.

Furthermore, among the five support members 232, the third supportmember is fixed so as not to rotate, while the other four supportmembers are all rotatable.

The sample 10S is held on the support member 232 so as not to move in awidth direction of the sample 10S. Note that, among the support members232, the support member 232 positioned between a light emitter 234 and alight receiver 235 and positioned substantially at the center betweenthe fixing portion 231 and a load applying portion has the slit 232A.Light L is irradiated from the light emitter 234 to the light receiver235 through the slit 232A. A slit width of the slit 232A is 1 mm and thelight L may pass through the width, without being blocked by the rim ofthe slit 232A.

Subsequently, after the measurement device is accommodated in a chambercontrolled in a predetermined environment controlled at a constanttemperature of 25° C. and a relative humidity of 50%, the weight 233 forapplying a load of 0.2 N is attached to the other end of the sample 10Sand the sample 10S is left for 2 hours in the environment. After 2hours, a width of the sample 10S is measured. Next, the weight forapplying the load of 0.2 N is changed to a weight for applying a load of0.6 N, and the width of the sample 10S is measured 5 minutes after theswitch. Finally, the weight is changed to a weight for applying a loadof 1.0 N, and the width of the sample 10S is measured 5 minutes afterthe switch.

As described above, by adjusting the weight of the weight 233, the loadapplied in the longitudinal direction of the sample 10S may be changed.With each load applied, light L is irradiated from the light emitter 234toward the light receiver 235, and the width of the sample 10S to whichthe load is applied in the longitudinal direction is measured. Themeasurement of the width is performed in a state where the sample 10S isnot curled. The light emitter 234 and the light receiver 235 areprovided in the digital dimension measuring instrument LS-7000.

(Thermal Expansion Coefficient α)

The thermal expansion coefficient α[ppm/° C.] of the magnetic recordingmedium 10 may be preferably 5.5 ppm/° C.≤α≤9 ppm/° C., and morepreferably 5.9 ppm/° C.≤α≤8 ppm/° C. When the thermal expansioncoefficient α is within the above range, a change in the width of themagnetic recording medium 10 may be further suppressed by adjustingtension in the longitudinal direction of the magnetic recording medium10 by the recording and reproducing apparatus.

The temperature expansion coefficient α is obtained as follows. First,the sample 10S is prepared in a manner similar to that of the method ofmeasuring the dimensional change amount Δw, the sample 10S is set in ameasurement device similar to that of the method of measuring thedimensional change amount Δw, and thereafter, the measurement device isaccommodated in a chamber of a predetermined environment controlled at atemperature of 29° C. and relative humidity of 24%. Next, a load of 0.2N is applied in the longitudinal direction of the sample 10S, and thesample 10S was placed in the above environment for 2 hours. Thereafter,with the relative humidity of 24% maintained, widths of the sample 10Sat 45° C., 29° C., and 10° C. are measured, while changing thetemperatures in order of 45° C., 29° C., and 10° C., and the temperatureexpansion coefficient α is obtained from the following equation. Here,the widths of the sample 10S are measured at these temperatures 2 hoursafter each temperature is reached.

Note that the measurement at the temperature of 29° C. is carried out inorder to check whether an abnormality has not occurred in themeasurement (in particular, to check whether these three measurementresults are linear) and the measurement results are not used in thefollowing equation.

$\begin{matrix}{{\alpha \left\lbrack {{ppm}/{{\,^{{^\circ}}\; C}.}} \right\rbrack} = {\frac{{{D\left( {45^{{^\circ}}\mspace{11mu} {C.}} \right)}\lbrack{mm}\rbrack} - {{D\left( {10^{{^\circ}}\mspace{11mu} {C.}} \right)}\lbrack{mm}\rbrack}}{{D\left( {10^{{^\circ}}\mspace{11mu} {C.}} \right)}\lbrack{mm}\rbrack} \times \frac{1,000,000}{\left( {45\left\lbrack {}^{{^\circ}}\mspace{11mu} {C.} \right\rbrack} \right) - \left( {10\left\lbrack {}^{{^\circ}}\mspace{11mu} {C.} \right\rbrack} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

(where, D(45° C.) and D(10° C.) represent the widths of the sample 10Sat the temperatures of 45° C. and 10° C., respectively).

(Humidity Expansion Coefficient β)

A humidity expansion coefficient β[ppm/% RH] of the magnetic recordingmedium 10 may be preferably β≤5.5 ppm/% RH, more preferably β≤5.2 ppm/%RH, and still more preferably β≤5.0 ppm/% RH. When the humidityexpansion coefficient β is within the range, a change in the width ofthe magnetic recording medium 10 can be further suppressed by adjustingtension in the longitudinal direction of the magnetic recording medium10 by the recording and reproducing apparatus.

The humidity expansion coefficient β is obtained as follows. First, thesample 10S is prepared in a manner similar to that of the method ofmeasuring the dimensional change amount Δw and set in a measurementdevice similar to that of the method of measuring the dimensional changeamount Δw, and thereafter, the measurement device is accommodated in achamber of a predetermined environment controlled at a temperature of29° C. and a relative humidity of 24%. Next, a load of 0.2 N is appliedin the longitudinal direction of the sample 10S, and the sample is leftin the environment for 2 hours. Thereafter, with the temperature of 29°C. maintained, widths of the sample 10S at relative humidity of 80%,24%, and 10% are measured, while the relative humidity is changed inorder of 80%, 24%, and 10%, and a humidity expansion coefficient β isobtained by the following equation. Here, the widths of the sample 10Sare measured at these pieces of humidity immediately after each humidityis reached. Note that the measurement at the humidity of 24% is carriedout in order to check whether an abnormality has not occurred in themeasurement, and the measurement results are not used in the followingequation.

$\begin{matrix}{{\beta \left\lbrack {{{ppm}/\%}\mspace{14mu} {RH}} \right\rbrack} = {\frac{{{D\left( {80\%} \right)}\lbrack{mm}\rbrack} - {{D\left( {10\%} \right)}\lbrack{mm}\rbrack}}{{D\left( {10\%} \right)}\lbrack{mm}\rbrack} \times \frac{1,000,000}{\left( {80\lbrack\%\rbrack} \right) - \left( {10\lbrack\%\rbrack} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

(where, D(80%) and D(10%) represent the widths of the sample 10S at therelative humidity 80% and 10%, respectively).

(Poisson's Ratio ρ)

A Poisson's ratio ρ of the magnetic recording medium 10 may bepreferably 0.25≤ρ, more preferably 0.29≤ρ, and still more preferably0.3≤ρ. When the Poisson's ratio ρ is within the above range, a change inthe width of the magnetic recording medium 10 can be further suppressedby adjusting tension in the longitudinal direction of the magneticrecording medium 10 by the recording and reproducing apparatus.

The Poisson's ratio ρ is obtained as follows. First, a ½ inch-widemagnetic recording medium 10 is prepared and cut into a length of 150 mmto prepare a sample, and a mark having a size of 6 mm×6 mm is given tothe center of the sample. Next, both end portions in the longitudinaldirection of the sample are chucked so that a distance between chucks is100 mm, an initial load of 2 N is applied, a length of the mark in thelongitudinal direction of the sample at that time is determined as aninitial length and a width of the mark in a width direction of thesample is determined as an initial width. Subsequently, the sample isstretched with an Instron type universal tensile tester at a tensilespeed of 0.5 mm/min and dimensional change amounts of the mark in thelength of the mark in the longitudinal direction of the sample and thewidth of the mark in the width direction of the sample are measured withan image sensor manufactured by Keyence Corporation. Thereafter,Poisson's ratio ρ is obtained from the following equation.

$\begin{matrix}{\rho = \frac{\left\{ \frac{\begin{pmatrix}{{Dimensional}\mspace{14mu} {Change}\mspace{14mu} {Amount}\mspace{14mu} {of}} \\{{Width}\mspace{14mu} {of}\mspace{14mu} {{Mark}\mspace{14mu}\lbrack{mm}\rbrack}}\end{pmatrix}}{\left( {{Initial}\mspace{14mu} {{Width}\mspace{14mu}\lbrack{mm}\rbrack}} \right)} \right\}}{\left\{ \frac{\begin{pmatrix}{{Dimensional}\mspace{14mu} {Change}\mspace{14mu} {Amount}\mspace{14mu} {of}} \\{{Length}\mspace{14mu} {of}\mspace{14mu} {{Mark}\mspace{14mu}\lbrack{mm}\rbrack}}\end{pmatrix}}{\left( {{Initial}\mspace{14mu} {{Length}\mspace{14mu}\lbrack{mm}\rbrack}} \right)} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

(Longitudinal Elasticity Limit Value Amp)

The elasticity limit value σ_(MD)[N] in the longitudinal direction ofthe magnetic recording medium 10 may be preferably 0.7 N≤σ_(MD), morepreferably 0.75 N≤σ_(MD), and still more preferably 0.8 N≤ρ_(MD). Whenthe elasticity limit value σ_(MD) is within the above range, a change inthe width of the magnetic recording medium 10 can be further suppressedby adjusting tension in the longitudinal direction of the magneticrecording medium 10 by the recording and reproducing apparatus.Furthermore, it is easier to control a drive side. An upper limit valueof the elasticity limit value σ_(MD) in the longitudinal direction ofthe magnetic recording medium 10 is not particularly limited and may be,for example, σ_(MD)≤5.0 N. Preferably, the elasticity limit value σ_(MD)does not depend on a speed V when an elastic limit is measured. Thereason is because, when the elastic limit value σ_(MD) does not dependon the speed V, the change in the width of the magnetic recording medium10 can be effectively suppressed without being affected by a runningspeed of the magnetic recording medium 10 in the recording andreproducing apparatus and a tension adjustment speed or responsivenessof the recording and reproducing apparatus. The elasticity limit valueσ_(MD) is set to a desired value, for example, depending on a selectionof curing conditions of the ground layer 12, the magnetic layer 13, andthe back layer 14, and or a selection of a material of the base layer11. For example, as a time for curing paint for forming the groundlayer, paint for forming the magnetic layer, and paint for forming theback layer is increased or as a curing temperature thereof is increased,a reaction between a binder and a curing agent contained in each paintis accelerated. As a result, elastic characteristic are improved toimprove the elasticity limit value σ_(MD).

The elastic limit value σ_(MD) is obtained as follows. First, a ½inch-wide magnetic recording medium 10 is prepared, cut into a length of150 mm to prepare a sample, and both ends of the sample in thelongitudinal direction are chuck in the universal tensile tester so thata distance λ₀ between the chucks is 100 mm (λ₀=100 mm). Next, the sampleis stretched at a tensile speed of 0.5 mm/min, and a load σ(N) regardingthe distance λ(mm) between the chucks is continuously measured.Subsequently, a relationship between Δλ(%) and σ(N) is graphed using theobtained data of λ(mm) and σ(N). However, Δλ(%) is given by thefollowing equation.

Δλ(%)=((λ−λ₀)/λ₀)×100

Next, in the above graph, a region in which the graph is a straight lineis calculated in the region of σ≥0.2 N and a maximum load a thereof isset as an elasticity limit value σ_(MD)(N).

(Friction Coefficient μ Between Magnetic Surface and Back Surface)

A friction coefficient μ between the surface of the magnetic layer sideand the surface of the back layer side of the magnetic recording medium10 (hereinafter, also referred to as interlayer friction coefficient μ)is preferably 0.20≤μ≤0.80, more preferably 0.20≤μ≤0.78, and still morepreferably 0.25≤μ≤0.75. When the friction coefficient μ is within theabove range, handling properties of the magnetic recording medium 10 isimproved. For example, when the friction coefficient μ is within theabove range, the occurrence of winding deviation when the magneticrecording medium 10 is wound around the reel (for example, the reel 10C,etc., in FIG. 5) is suppressed. More specifically, in a case where thefriction coefficient μ is too small (for example, in case of μ<0.18), aninterlayer friction between a magnetic surface of a portion of themagnetic recording medium 10, which has already been wound around thecartridge reel, positioned on the outermost circumference and a backsurface of the magnetic recording medium 10 to be newly wound around anouter side thereof is extremely low and thus the magnetic recordingmedium 10 to be newly wound may readily deviate from the magneticsurface of the portion position on the outermost circumference of themagnetic recording medium 10 which has already been wound. Therefore,winding deviation of the magnetic recording medium 10 occurs. Meanwhile,in a case where the friction coefficient μ is too large (for example, incase of 0.82<μ or 0.80<μ), an interlayer friction between the backsurface of the magnetic recording medium 10 which is to be definitelyreleased from the outermost circumference of the reel on the drive sideand the magnetic surface of the magnetic recording medium 10, which ispositioned immediately thereunder and which is in a state of being woundyet on the reel on the drive side is extremely high, so the back surfaceand the magnetic surface are stuck to each other. Therefore, theoperation of the magnetic recording medium 10 toward the cartridge reelbecomes unstable, thereby causing winding deviation of the magneticrecording medium 10.

The friction coefficient μ is obtained as follows. First, the magneticrecording medium 10 having a width of ½ inches, with the back surfacefacing upward, is wound around a circumference having a diameter of 1inch so as to be fixed. Next, the magnetic recording medium 10 havingthe width of ½ inches is brought into contact with the circumference ata wrap angle of θ(°)=180°+1° to 180°−10° so that the magnetic surfacethereof is in contact therewith and one end of the magnetic recordingmedium 10 is connected to a movable strain gauge and tension T₀=0.6(N)is given to the other end of the magnetic recording medium 10. Thereading T₁(N) to T₈(N) of the movable strain gauge at each outward pathwhen the movable strain gauge is reciprocated 8 times at 0.5 mm/s ismeasured, and an average value of T₄ to T₈ is determined as T_(ave)(N).Thereafter, the friction coefficient μ is obtained from the followingequation.

$\begin{matrix}{\mu = {\frac{1}{\left( {\theta \lbrack{^\circ}\rbrack} \right) \times \left( {\pi/180} \right)} \times {\log_{e}\left( \frac{T_{ave}\lbrack N\rbrack}{T_{0}\lbrack N\rbrack} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

(Surface Roughness R_(ab) of Back Layer)

The surface roughness R_(ab)[nm] (in other words, a surface roughness ofthe back surface) of the back layer 14 is preferably 7.5 nm or less,more preferably 7.2 nm or less, still more preferably 7.0 nm or less,6.5 nm or less, 6.3 nm or less, or 6.0 nm or less. Furthermore, thesurface roughness R_(ab) is preferably 3.0 nm or more, more preferably3.2 nm or more, and still more preferably 3.4 nm or more. When thesurface roughness R_(ab) of the back layer is within the above range,handling properties of the magnetic recording medium 10 can be improved.

Furthermore, when the magnetic recording medium 10 is wound, aninfluence on the surface of the magnetic layer can be reduced, and thus,an adverse effect on the electromagnetic conversion characteristic canbe suppressed. The handling properties and electromagnetic conversioncharacteristic are contradictory properties, but the surface roughnessR_(ab) within the numerical range enables their compatibility.

The surface roughness R_(ab) of the back surface is obtained as follows.First, the magnetic recording medium 10 having a width of ½ inches isprepared, and the magnetic recording medium 10 is attached to a slideglass, with the back surface facing upward (that is, the magneticsurface is attached to the slide glass) to use it as a sample piece.Next, a surface roughness of the back surface of the sample piece ismeasured by the following non-contact roughness meter using opticalinterference.

Device: Non-contact roughness meter using optical interference

(VertScan R5500GL-M100-AC, non-contact surface and layer cross-sectionalshape measurement system, manufactured by Ryoka Systems Inc.)

Objective lens: 20 times (approximately 237 μm×178 μm field of view)

Resolution: 640 points×480 points

Measurement mode: phase

Wavelength filter: 520 nm

Surface correction: correction by quadratic polynomial approximationplane

As described above, a surface roughness is measured at positions of atleast five spots in the longitudinal direction, and an average value ofeach arithmetic average roughness Sa(nm), which is automaticallycalculated from a surface profile obtained at each position, isdetermined as the surface roughness R_(ab)(nm) of the back surface.

(Width Deformation Coefficient b)

A width deformation coefficient b during long-term storage in a casewhere a long-term storage width change amount Y of the magneticrecording medium 10 is defined as Y=blog(t) is −0.06 μm≤b≤0.06 μm. Whenthe width deformation coefficient b is within the above numerical range,the suitability for use in the recording and reproducing apparatus doesnot change even in a case where the magnetic recording medium is storedfor a long period of time. Therefore, for example, a phenomenonundesirable for magnetic recording, such as an off-track phenomenon,does not easily occur.

A method of calculating the width deformation coefficient b will bedescribed with reference to FIGS. 11A to 11C. FIG. 11A is a schematicdiagram of a data band and a servo band formed in a magnetic layer of amagnetic recording tape. As shown in FIG. 11A, the magnetic layer hasfour data bands d0 to d3. The magnetic layer has a total of five servobands S0 to S4 so that each data band is sandwiched by two servo bands.As shown in FIG. 11B, each servo band has repeated frame units eachincluding five servo signals S5 a inclined at a predetermined angle θ1,five servo signals S5 b inclined at the same angle in the oppositedirection of the servo signals S5 a, four servo signals S4 a inclined atthe predetermined angle θ1, and four servo signals S4 b inclined at thesame angle in the opposite direction of the servo signals S4 a. Theangle θ1 may be, for example, 5° to 25°, and particularly 11° to 20°.

The width deformation coefficient b is obtained from the deviationamount of the servo track width measured by the following method.

The deviation amount of the servo track width refers to an amount ofdeviation of a position of a center line of each servo band when theposition of the center line of each servo band with respect to a servolead head of the magnetic recording and reproducing apparatus deviatesfrom a standard position due to a change in width of the magneticrecording medium. The standard position is a position of the center lineof each servo band, in a case where the magnetic recording medium 10 hasa standard servo track width.

Measurement of the deviation amount of the servo track width isperformed while causing the magnetic recording medium to run to be drawninto the magnetic recording and reproducing apparatus (that is, whilecausing the magnetic recording medium to run in a forward direction).The deviation amount of the servo track width used to obtain the widthdeformation coefficient b is a deviation amount of two servo tracks S1and S2 sandwiching a second data band d1 from the top of FIG. 11Atherebetween.

In a case where two servo tracks S1 and S2 sandwiching the data band d1are reproduced at the time of driving, a waveform as shown in FIG. 11Cis obtained for each servo track by a digital oscilloscope (WAVEPRO 960manufactured by Lecroy Corporation).

A time between the timing signals is obtained from the waveform obtainedby reproduction of the servo track S1 and a distance between a leadingmagnetic stripe of burst A and a leading magnetic stripe of burst B inthe servo track S1 is calculated from the time and a tape running speed.For example, as shown in FIG. 11B, a distance L1 between a leadingmagnetic stripe (the leftmost magnetic stripe among the five magneticstripes) of the burst A S5 a-1 and a leading magnetic stripe (theleftmost magnetic stripe among the five magnetic stripes) of the burst BS5 b-1 is calculated.

Similarly, a time between timing signals is obtained from a waveformobtained by reproduction of the servo track S2, and a distance betweenthe leading magnetic stripe of the burst A and the leading magneticstripe of the burst B in the servo track S2 is calculated from the timeand a tape running speed. For example, as shown in FIG. 11B, a distanceL2 between a leading magnetic stripe of the burst A S5 a-2 and a leadingmagnetic stripe of the burst B S5 b-2 is calculated. For example, in acase where the magnetic recording tape is enlarged in the widthdirection, for example, a time between timing signals obtained byreproduction of the servo track S1 is lengthened, and as a result, thecalculated distance L1 may also be increased. In a case where themagnetic recording tape is reduced in the width direction, thecalculated distance L1 may be reduced. Therefore, by using the distanceL1, the distance L2 and an azimuth angle, the deviation amount of theservo track width may be obtained. The deviation amount of the servotrack width is obtained from the following equation.

(Deviation amount of servo track width)={(L1−L2)/2}×tan(90°−θ1)

In this equation, L1 and L2 are the distances L1 and L2 described above,and θ1 is the inclination angle θ1 described above and is also referredto as an azimuth angle. θ1 is obtained by developing the magneticrecording tape taken out from the cartridge with FERRICOLLOID developerand using a universal tool microscope (TOPCON TUM-220ES) and a dataprocessing device (TOPCON CA-1B).

The deviation amount of the servo track width is a change amount withrespect to a standard servo track width. The standard servo track widthmay be equal to the servo lead head width of the magnetic recording andreproducing apparatus and may be determined, for example, according tothe type of the magnetic recording medium 10 such as a standard that themagnetic recording medium 10 follows, and the like.

The magnetic recording tape is stored under an environment of 32° C. and55% for 300 hours, and a deviation amount of the servo track width ismeasured at an interval of about every 50 m over the entire length of arange excluding 20 m from the outer side and inner side of the windingof the magnetic recording tape at an interval of 50 hours during thestorage for 300 hours. In the present specification, “outer side ofwinding” refers to an end portion of the magnetic recording mediumpositioned on an outer side when the magnetic recording medium is woundin the magnetic recording cartridge, among two end portions of themagnetic recording medium. Meanwhile, “inner side of winding” refers toan end portion of the magnetic recording medium mounted on a reel(around which the magnetic recording medium is wound) inside themagnetic recording cartridge, among two end portions of the magneticrecording medium.

In consideration of the above circumstances, a deviation amount of theservo track width at each position of the magnetic recording tape storedfor 50 hours under the environment of 32° C. and 55% as a referencevalue, a change amount (long-term storage width change amount Y) of thedeviation amount of the servo track width from the reference value whenthe magnetic recording tape is stored for t time (t≥50) is obtained. Thewidth deformation coefficient b in a case where the long-term storagewidth change amount Y is defined as Y=blog(t) is obtained using theleast squares method from the relationship between the long-term storagewidth change amount Y and the storage time.

The long-term storage width change amount Y when stored for a certainperiod under the environment of 32° C. and 55% may be obtained from aformula regarding Y, using the width deformation coefficient b and thetime t obtained as described above. For example, the long-term storagewidth change amount Y after storage for 10 years may be obtained fromthe following formula.

(Long-term storage width change amount Y after 10-year storage)=blog {10(years)×365 (days)×24 (hours)}

Note that the width deformation coefficient b can be adjusted, forexample, as follows. In order to alleviate distortion occurring in themagnetic recording medium 10, winding tension may be lowered in a dryingprocess of the magnetic recording medium 10 and/or a calendering process(heating region). Furthermore, in order to alleviate distortion in apancake state and/or a cartridge state after cutting, the magneticrecording medium 10 may be stored for a long time at a temperature of55° C. or higher. In this manner, the width deformation coefficient bcan be adjusted by alleviating distortion.

(Coercive Force Hc)

The coercive force Hc measured in the thickness direction (verticaldirection) of the magnetic recording medium 10 is preferably 220 kA/m to310 kA/m, more preferably 230 kA/m to 300 kA/, still more preferably 240kA/m to 290 kA/m. When the coercive force Hc is 220 kA/m or more, thecoercive force Hc becomes a sufficient magnitude, and thus, adegradation of a magnetic signal recorded on an adjacent track due to aleakage magnetic field from the recording head may be suppressed.Therefore, a better SNR can be obtained. On the other hand, when thecoercive force Hc is 310 kA/m or less, saturation recording by therecording head is facilitated, and thus, a better SNR can be obtained.

The coercive force Hc is obtained as follows. First, a measurementsample is cut out from the long-shaped magnetic recording medium 10 andan M-H loop of the entire measurement sample is measured in thethickness direction of the measurement sample (thickness direction ofthe magnetic recording medium 10) using a vibrating sample magnetometer(VSM). Next, the coating film (ground layer 12, magnetic layer 13, etc.)is wiped out using acetone, ethanol, or the like, to leave only the baselayer 11 for background correction, and the M-H loop of the base layer11 is measured in the thickness direction of the base layer 11 (thethickness direction of the magnetic recording medium 10) using the VSM.Thereafter, the M-H loop of the base layer 11 is subtracted from the M-Hloop of the entire measurement sample to obtain an M-H loop afterbackground correction. The coercive force Hc is obtained from theobtained M-H loop. Note that it is assumed that the measurement of theM-H loop is entirely performed at 25° C.

Furthermore, it is also assumed that “demagnetizing field correction”when the M-H loop is measured in the thickness direction (verticaldirection) of the magnetic recording medium 10 is not performed.

(Ratio R of Coercive Force Hc(50) and Coercive Force Hc(25))

The ratio R (=(Hc(50)/Hc(25))×100) between the coercive force Hc(50)measured at 50° C. in the thickness direction (vertical direction) ofthe magnetic recording medium 10 to the coercive force Hc(25) measuredat 25° C. in the thickness direction of the magnetic recording medium 10is preferably 95% or more, more preferably 96% or more, still morepreferably 97% or more, and particularly preferably 98% or more. Whenthe ratio R is 95% or more, temperature dependence of the coercive forceHc is small, and thus, deterioration of the SNR under a high temperatureenvironment can be suppressed.

The coercive force Hc(25) is obtained in a manner similar to the methodof measuring the coercive force Hc. Furthermore, the coercive forceHc(50) is obtained in a manner similar to the method of measuring thecoercive force Hc except that the M-H loops of the measurement sampleand the base layer 11 are all measured at 50° C.

(Squareness Ratio S1 Measured in Longitudinal Direction)

The squareness ratio S1 measured in the longitudinal direction (runningdirection) of the magnetic recording medium 10 is preferably 35% orless, more preferably 27% or less, and still more preferably 20% orless. When the squareness ratio S1 is 35% or less, vertical alignment ofthe magnetic powder is sufficiently high, and therefore, a better SNRcan be obtained.

Therefore, better electromagnetic conversion characteristic can beobtained. Furthermore, a shape of the servo signal is improved, andthus, the control on the drive side may be performed more easily.

In this specification, the perpendicular alignment of the magneticrecording medium may mean that the squareness ratio S1 of the magneticrecording medium is within the above numerical range (for example, 35%or less). The magnetic recording medium according to the embodiment ofthe present technology is preferably perpendicularly aligned.

The squareness ratio S1 is obtained as follows. First, a measurementsample is cut out from a long-shaped magnetic recording medium 10, andan M-H loop of the entire measurement sample corresponding to thelongitudinal direction (running direction) of the magnetic recordingmedium 10 is measured using the VSM. Next, the coating film (groundlayer 12, magnetic layer 13, etc.) is wiped out using acetone, ethanol,or the like, to leave only the base layer 11 for background correction,and the M-H loop of the base layer 11 corresponding to the longitudinaldirection of the base layer 11 (running direction of the magneticrecording medium 10) is measured using the VSM. Thereafter, the M-H loopof the base layer 11 is subtracted from the M-H loop of the entiremeasurement sample to obtain an M-H loop after background correction.The squareness ratio S1(%) is calculated by substituting a saturationmagnetization Ms(emu) and residual magnetization Mr(emu) of the obtainedM-H loop into the following equation. Note that it is assumed that themeasurement of the M-H loop is entirely performed at 25° C.

Squareness ratio S1(%)=(Mr/Ms)×100

(Squareness Ratio S2 Measured in Vertical Direction)

The squareness ratio S2 measured in the vertical direction (thicknessdirection) of the magnetic recording medium 10 is preferably 65% ormore, more preferably 73% or more, and still more preferably 80% ormore. When the squareness ratio S2 is 65% or more, vertical alignment ofthe magnetic powder is sufficiently high, and thus, a better SNR can beobtained. Therefore, better electromagnetic conversion characteristiccan be obtained. Furthermore, a servo signal shape is improved, makingit easier to control a drive side.

In this specification, the perpendicular alignment of the magneticrecording medium may mean that the squareness ratio S2 of the magneticrecording medium is within the above numerical range (for example, 65%or more).

The squareness ratio S2 is obtained in a similar manner to thesquareness ratio S1 except that the M-H loops are measured in thevertical direction (thickness direction) of the magnetic recordingmedium 10 and the base layer 11. Note that, in the measurement of thesquareness ratio S2, it is assumed that “demagnetizing field correction”when measuring the M-H loop is measured in the vertical direction of themagnetic recording medium 10 is not performed.

The squareness ratios S1 and S2 may be set to a desired value byadjusting, for example, strength of a magnetic field applied to themagnetic layer forming coating material, an application time of themagnetic field to the magnetic layer forming coating material, adispersion state of the magnetic powder in the magnetic layer formingcoating material, and a concentration of the solid content in themagnetic layer forming coating material. Specifically, for example, asthe strength of the magnetic field is increased, the squareness ratio S1is reduced, while the squareness ratio S2 is increased. Furthermore, asthe application time of the magnetic field is longer, the squarenessratio S1 is reduced, while the squareness ratio S2 is increased.

Furthermore, as the dispersion state of the magnetic powder is improved,the squareness ratio S1 is reduced, while the squareness ratio S2 isincreased. Furthermore, as the concentration of the solid content islowered, the squareness ratio S1 is reduced, while the squareness ratioS2 is increased. Note that the above adjustment method may be used aloneor in combination of two or more.

(SFD)

In a switching field distribution (SFD) curve of the magnetic recordingmedium 10, a peak ratio X/Y of a main peak height X and a height Y of asub peak in the vicinity of magnetic field zero is preferably 3.0 ormore, more preferably 5.0 or more, still more preferably 7.0 or more,particularly preferably 10.0 or more, and most preferably 20.0 or more(see FIG. 4). When the peak ratio X/Y is 3.0 or more, it is possible tosuppress inclusion of a large amount of coercive force component (forexample, soft magnetic particles, superparamagnetic particles, etc.)unique to ε iron oxide other than the ε iron oxide particlescontributing to actual recording in the magnetic powder. Therefore,deterioration of magnetization signals recorded on the adjacent tracksdue to a leakage magnetic field from the recording head is suppressed,and thus, a better SNR can be obtained. An upper limit value of the peakratio X/Y is not particularly limited, but is, for example, 100 or less.

The peak ratio X/Y is obtained as follows. First, an M-H loop afterbackground correction is obtained in a manner similar to the method ofmeasuring the coercive force Hc described above. Next, an SFD curve iscalculated from the obtained M-H loop. The calculation of the SFD curvemay be performed by using a program attached to the measurement device,or by using other programs. Assuming that an absolute value of a pointat which the calculated SFD curve traverses the Y axis (dM/dH) is “Y”and a height of the main peak seen in the vicinity of the coercive forceHc in the M-H loop is “X”, a peak ratio X/Y is calculated. Note that themeasurement of the M-H loop is performed at 25° C. in a manner similarto the method of measuring the coercive force Hc described above.Furthermore, it is also assumed that “demagnetizing field correction”when the M-H loop is measured in the thickness direction (verticaldirection) of the magnetic recording medium 10 is not performed.

(Activation Volume V_(act))

The activation volume V_(act) is preferably 8000 nm³ or less, morepreferably 6000 nm³ or less, still more preferably 5000 nm³ or less,particularly preferably 4000 nm³ or less, and most preferably 3000 nm³or less. When the activation volume V_(act) is 8000 nm³ or less, thedispersion state of the magnetic powder is improved, and thus, a bitreversal region can be made steep and a degradation of the magnetizationsignal recorded on the adjacent track due to a leakage magnetic fieldfrom the recording head may be suppressed. Therefore, there is apossibility that a better SNR may not be obtained.

The activation volume V_(act) is obtained by the following formuladerived by Street&Woolley.

V _(act)(nm³)=k _(B) ×T×X _(irr)/(μ₀ ×Ms×S)

(where, k_(B): Boltzmann constant (1.38×10⁻²³ J/K), T: temperature (K),X_(irr): irreversible magnetic susceptibility, μ₀: permeability ofvacuum, S: magnetic viscosity coefficient, Ms: saturation magnetization(emu/cm³))

The irreversible magnetic susceptibility X_(irr), the saturationmagnetization Ms and the magnetic viscosity coefficient S substituted inthe above formula are obtained as follows using the VSM. Note that themeasurement direction by the VSM is the thickness direction (verticaldirection) of the magnetic recording medium 10. Furthermore, it isassumed that the measurement by the VSM is performed at 25° C. for themeasurement sample cut out from the long-shaped magnetic recordingmedium 10. Furthermore, it is also assumed that “demagnetizing fieldcorrection” when the M-H loop is measured in the thickness direction(vertical direction) of the magnetic recording medium 10 is notperformed.

(Irreversible Magnetic Susceptibility X_(irr))

The irreversible magnetic susceptibility X_(irr) is defined as aninclination in the vicinity of the residual coercive force Hr in theinclination of the residual magnetization curve (DCD curve). First, amagnetic field of −1193 kA/m (15 kOe) is applied to the entire magneticrecording medium 10, and the magnetic field is returned to zero to entera residual magnetization state. Thereafter, a magnetic field of about15.9 kA/m (200 Oe) is applied in the opposite direction, and themagnetic field is returned again to zero and a residual magnetizationamount is measured. Thereafter, similarly, a measurement of applying amagnetic field 15.9 kA/m larger than the immediately previously appliedmagnetic field and returning the magnetic field to zero is repeatedlyperformed, and a DCD curve is measured by plotting a residualmagnetization amount against the applied magnetic field. From theobtained DCD curve, the point at which the magnetization amount is zerois set as the residual coercive force Hr, and an inclination of the DCDcurve in each magnetic field is obtained by differentiating the DCDcurve again. In the inclination of the DCD curve, the inclination nearthe residual coercive force Hr is X_(irr).

(Saturation Magnetization Ms)

First, an M-H loop of the entire magnetic recording medium 10(measurement sample) is measured in the thickness direction of themagnetic recording medium 10. Next, the coating film (ground layer 12,magnetic layer 13, etc.) is wiped out using acetone, ethanol, or thelike, to leave only the base layer 11 for background correction, and theM-H loop of the base layer 11 is measured in the thickness direction ofthe base layer 11 similarly. Thereafter, the M-H loop of the base layer11 is subtracted from the M-H loops of the entire magnetic recordingmedium 10 to obtain an M-H loop after background correction. Ms(emu/cm³) is calculated from the value of the saturation magnetizationMs (emu) of the obtained M-H loop and the volume (cm³) of the magneticlayer 13 in the measurement sample. Note that the volume of the magneticlayer 13 is obtained by multiplying the area of the measurement sampleby the average thickness of the magnetic layer 13. A method ofcalculating the average thickness of the magnetic layer 13 necessary forcalculating the volume of the magnetic layer 13 will be described later.

(Magnetic Viscosity Coefficient S)

First, a magnetic field of −1193 kA/m(15 kOe) is applied to the entiremagnetic recording medium 10 (measurement sample), and the magneticfield is returned to zero to enter a residual magnetization state.Thereafter, in the opposite direction, a magnetic field equivalent tothe value of the residual coercive force Hr obtained from the DCD curveis applied. With the magnetic field applied, the magnetization amount iscontinuously measured at constant time intervals for 1000 seconds. Arelationship between the time t and the magnetization amount M(t) thuslyobtained is compared with the following equation to calculate themagnetic viscosity coefficient S.

M(t)=M0+S×ln(t)

(where M(t): magnetization amount at time t, M0: initial magnetizationamount, S: magnetic viscosity coefficient, ln(t): natural logarithm oftime)

(Arithmetic Mean Roughness Ra)

The arithmetic mean roughness Ra of the magnetic surface is preferably2.5 nm or less, and more preferably 2.0 nm or less. When Ra is 2.5 nm orless, a better SNR can be obtained.

The arithmetic mean roughness Ra is obtained as follows. First, thesurface of the side on which the magnetic layer 13 is provided isobserved using an atomic force microscope (AFM) (Dimension Iconmanufactured by Bruker Corporation) to obtain a cross-sectional profile.

Next, the arithmetic mean roughness Ra is obtained from the obtainedcross-sectional profile in accordance with JIS B0601: 2001.

(4) Method of Manufacturing Magnetic Recording Medium

Next, a method of manufacturing the magnetic recording medium 10 havingthe above-described configuration will be described. First, a groundlayer-forming coating material is prepared by kneading and/or dispersinga non-magnetic powder, a binder, or the like, in a solvent. Next, themagnetic layer-forming coating material is prepared by kneading and/ordispersing the magnetic powder and the binder in a solvent. For thepreparation of the magnetic layer-forming coating material and theground layer-forming coating material, for example, the followingsolvents, a dispersing device and a kneading device may be used.

Examples of the solvents used for preparing the above-described coatingmaterial include ketone solvents such as acetone, methyl ethyl ketone,methyl isobutyl ketone, cyclohexanone, and the like; alcohol solventssuch as methanol, ethanol and propanol; ester solvents such as methylacetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,ethylene glycol acetate, and the like; ether solvents such as diethyleneglycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, andthe like; aromatic hydrocarbon solvents such as benzene, toluene andxylene; and halogenated hydrocarbon solvents such as methylene chloride,ethylene chloride, carbon tetrachloride, chloroform, chlorobenzene, andthe like. One of these may be used, or a mixture of two or more thereofmay be used.

As the kneading device used in the preparation of the coating materialpreparation described above, for example, a kneading device such as acontinuous biaxial kneader, a continuous biaxial kneader capable ofdiluting in multiple steps, a kneader, a press kneader, and a rollkneader may be used but the present technology is not particularlylimited thereto. Furthermore, examples of the dispersing device used inthe preparation of the coating material preparation described aboveinclude roll mills, ball mills, horizontal sand mills, vertical sandmills, spike mills, pin mills, tower mills, pearl mills (for example,DCP Mill, manufactured by Nippon Eirich Co., Ltd., etc.), a homogenizer,an ultrasonic dispersing device, or the like, may be used, but thepresent technology is not particularly limited thereto.

Next, the ground layer-forming coating material is applied to one mainsurface of the base layer 11 and dried to form the ground layer 12.Subsequently, the magnetic layer-forming coating material is applied tothe ground layer 12 and dried to form the magnetic layer 13 on theground layer 12. Note that, at the time of drying, magnetic powder ismagnetically aligned in the thickness direction of the base layer 11 by,for example, a solenoid coil. Furthermore, at the time of drying, forexample, the magnetic powder may be magnetically aligned in thelongitudinal direction (running direction) of the base layer 11 and thenmagnetically aligned in the thickness direction of the base layer 11 bya solenoid coil. After the formation of the magnetic layer 13, the backlayer 14 is formed on the other main surface of the base layer 11.

Accordingly, the magnetic recording medium 10 is obtained.

Thereafter, the obtained magnetic recording medium 10 is wound around alarge-diameter core again and a curing treatment is performed thereon.Finally, calendering is performed on the magnetic recording medium 10,and thereafter, the magnetic recording medium 10 is cut into apredetermined width (for example, ½ inch width). As a result, a magneticrecording medium 10 of a desired long-shaped may be obtained.

(5) Recording and Reproducing Apparatus

[Configuration of Recording and Reproducing Apparatus]

Next, an example of a configuration of a recording and reproducingapparatus 30 for performing recording and reproducing on the magneticrecording medium 10 having the above-described configuration will bedescribed with reference to FIG. 5.

The recording and reproducing apparatus 30 has a configuration capableof adjusting tension applied in the longitudinal direction of themagnetic recording medium 10. Furthermore, the recording and reproducingapparatus 30 has a configuration allowing the magnetic recording mediumcartridge 10A to be loaded therein. Here, in order to facilitate thedescription, a case where the recording and reproducing apparatus 30 hasa configuration allowing one magnetic recording medium cartridge 10A tobe loaded therein will be described, but the recording and reproducingapparatus 30 may be configured so that a plurality of magnetic recordingmedium cartridges 10A may be loaded therein.

The recording and reproducing apparatus 30 is preferably a timing servotype magnetic recording and reproducing apparatus. The magneticrecording medium according to the embodiment of the present technologyis suitable for use in a timing servo type magnetic recording andreproducing apparatus.

The recording and reproducing apparatus 30 is connected to aninformation processing device such as a server 41 and a personalcomputer (hereinafter referred to as “PC”) 42 via a network 43, and isconfigured to record data supplied from these information processingdevices in the magnetic recording medium cartridge 10A. The shortestrecording wavelength of the recording and reproducing apparatus 30 ispreferably 100 nm or less, more preferably 75 nm or less, still morepreferably 60 nm or less, and particularly preferably 50 nm or less.

As illustrated in FIG. 5, the recording and reproducing apparatusincludes a spindle 31, a reel 32 on the recording and reproducingapparatus side, a spindle driving device 33, a reel driving device 34, aplurality of guide rollers 35, a head unit 36, a communication interface(I/F) 37, and a control device 38.

The spindle 31 is configured to mount the magnetic recording mediumcartridge 10A. The magnetic recording medium cartridge 10A is compliantwith the linear tape open (LTO) standard and rotatably accommodates asingle reel 10C, around which the magnetic recording medium 10 is woundto be mounted, in a cartridge case 10B. In the magnetic recording medium10, an inverted V-shaped servo pattern is recorded in advance as a servosignal. The reel 32 is configured to fix a leading end of the magneticrecording medium 10 drawn out from the magnetic recording mediumcartridge 10A.

The embodiment of the present technology also provides a magneticrecording cartridge including a magnetic recording medium according tothe present technology. In the magnetic recording cartridge, themagnetic recording medium may be wound around, for example, a reel. Thespindle driving device 33 is a device for rotationally driving thespindle 31. The reel driving device 34 is a device for rotationallydriving the reel 32. When data is recorded to or reproduced from themagnetic recording medium 10, the spindle driving device 33 and the reeldriving device 34 rotationally drive the spindle 31 and the reel 32 tocause the magnetic recording medium 10 to run. The guide roller 35 is aroller for guiding running of the magnetic recording medium 10.

The head unit 36 includes a plurality of recording heads for recordingdata signals to the magnetic recording medium 10, a plurality ofreproducing heads for reproducing the data signals recorded on themagnetic recording medium 10, and a plurality of servo heads forreproducing a servo signal recorded on the magnetic recording medium 10.As the recording head, for example, a ring type head may be used, butthe type of the recording head is not limited thereto. The communicationI/F 37 is for communicating with the information processing device suchas the server 41 and the PC 42, and is connected to the network 43.

The control device 38 controls the entire recording and reproducingapparatus 30. For example, the control device 38 records the data signalsupplied from the information processing device such as the server 41 orthe PC 42 to the magnetic recording medium 10 by the head unit 36 inresponse to a request from the information processing device.Furthermore, the control device 38 reproduces the data signal recordedon the magnetic recording medium 10 by the head unit 36 and supplies thereproduced data signal to the information processing apparatus, inresponse to the request from the information processing apparatus suchas the server 41 and the PC 42. Furthermore, the control device 38detects a change in width of the magnetic recording medium 10 on thebasis of the servo signal supplied from the head unit 36. Morespecifically, the magnetic recording medium 10 has a plurality ofinverted V-shaped servo patterns recorded as servo signals thereon andthe head unit 36 simultaneously reproduces two different servo patternsby the two servo heads on the head unit 36 and obtain each servo signal.A position of the head unit 36 is controlled to follow the servo patternusing the servo pattern and relative position information of the headunit obtained from this servo signal. At the same time, distanceinformation between the servo patterns may be obtained by comparing thetwo servo signal waveforms. By comparing the distance informationbetween the servo patterns obtained at the time of each measurement, achange in distance between the servo patterns at the time of eachmeasurement may be obtained. By adding the distance information betweenthe servo patterns at the time of servo pattern recording, a change inthe width of the magnetic recording medium 10 may also be calculated.The control device 38 adjusts tension in a longitudinal direction of themagnetic recording medium 10 so that the width of the magnetic recordingmedium 10 is a defined width or a substantially defined width bycontrolling rotation driving of the spindle driving device 33 and thereel driving device 34 on the basis of the change in the distancebetween the servo patterns obtained as described above or the calculatedwidth of the magnetic recording medium 10. Accordingly, a change in thewidth of the magnetic recording medium 10 may be suppressed.

[Operation of Recording and Reproducing Apparatus]

Next, the operation of the recording and reproducing apparatus 30 havingthe above-described configuration will be described.

First, the magnetic recording medium cartridge 10A is attached to therecording and reproducing apparatus 30, a leading end of the magneticrecording medium 10 is drawn out and transferred to the reel 32 throughthe plurality of guide rollers 35 and the head unit 36, and the leadingend of the magnetic recording medium 10 is installed on the reel 32.

Next, when an operation unit (not shown) is operated, the spindledriving device 33 and the reel driving device 34 are driven under thecontrol of the control device 38, and the spindle 31 and the reel 32 arerotated in the same direction so that the magnetic recording medium 10runs from the reel 10C toward the reel 32. As a result, while themagnetic recording medium 10 is being wound around the reel 32,information is recorded on the magnetic recording medium 10 orinformation recorded on the magnetic recording medium 10 is reproducedby the head unit 36.

Furthermore, in a case where the magnetic recording medium 10 is rewoundaround the reel 10C, the spindle 31 and the reel 32 are rotationallydriven in a direction opposite to the above direction such that themagnetic recording medium 10 runs from the reel 32 to the reel 10C.Also, at the time of rewinding, the information is recorded on themagnetic recording medium 10 or the information recorded on the magneticrecording medium 10 is reproduced by the head unit 36.

(6) Effect

In the magnetic recording medium 10 according to the first embodiment,an average thickness t_(T) of the magnetic recording medium 10 ist_(T)≤5.6 μm, a dimensional change amount Δw of the magnetic recordingmedium 10 in the width direction with respect to a change in tension ofthe magnetic recording medium 10 in the longitudinal direction is 660ppm/N≤Δw, a squareness ratio in the vertical direction is 65% or more,and a width deformation coefficient b during long-term storage in a casewhere a long-term storage width change amount Y is defined as Y=blog(t)is −0.06 μm≤b≤0.06 μm. Accordingly, a change in the width of themagnetic recording medium 10 can be suppressed by adjusting tension ofthe magnetic recording medium 10 in the longitudinal direction by therecording and reproducing apparatus. For example, even if there is achange in temperature and humidity that may cause a change in the widthof the magnetic recording medium 10, the width of the magnetic recordingmedium 10 can be kept constant or substantially constant. The change inwidth by the tension adjustment may be suppressed even after long-termstorage. In addition, although the magnetic recording medium 10 is asthin as t_(T)≤5.6 μm, the magnetic recording medium 10 is excellent inhandling properties.

(7) Modification

[Modification 1]

The magnetic recording medium 10 may further include a barrier layer 15provided on at least one surface of the base layer 11 as shown in FIG.7. The barrier layer 15 is a layer for suppressing a dimensional changein the base layer 11 depending on the environment. For example, moistureabsorbency of the base layer 11 is an example of a cause of thedimensional change, and a penetration speed of moisture into the baselayer 11 may be reduced by the barrier layer 15. The barrier layer 15includes a metal or a metal oxide. As the metal, for example, at leastone of Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y, Zr, Mo,Ru, Pd, Ag, Ba, Pt, Au, or Ta may be used. As the metal oxide, forexample, at least one of Al₂O₃, CuO, CoO, SiO₂, Cr₂O₃, TiO₂, Ta₂O₅ orZrO₂ may be used, and any of the oxides of the above metals may also beused. Furthermore, diamond-like carbon (DLC), diamond, and the like mayalso be used.

An average thickness of the barrier layer 15 is preferably 20 nm to 1000nm, and more preferably 50 nm to 1000 nm. The average thickness of thebarrier layer 15 is obtained in a manner similar to the averagethickness t_(m) of the magnetic layer 13. However, a magnification ofthe TEM image is appropriately adjusted according to thicknesses of thebarrier layer 15.

[Modification 2]

The magnetic recording medium 10 may be incorporated in a libraryapparatus. In other words, the present technology also provides alibrary apparatus including at least one magnetic recording medium 10.The library apparatus has a configuration capable of adjusting tensionapplied in the longitudinal direction of the magnetic recording medium10, and may include a plurality of the recording and reproducingapparatuses 30 described above.

[Modification 3]

The magnetic recording medium 10 may be attached to servo signal writeprocessing by a servo writer. The servo writer may adjust tension in thelongitudinal direction of the magnetic recording medium 10 whenrecording a servo signal or the like, thereby keeping the width of themagnetic recording medium 10 constant or substantially constant. In thiscase, the servo writer may have a detection device for detecting thewidth of the magnetic recording medium 10. The servo writer may adjustthe tension in the longitudinal direction of the magnetic recordingmedium 10 on the basis of a detection result from the detection device.

3. SECOND EMBODIMENT (EXAMPLE OF VACUUM THIN FILM TYPE MAGNETICRECORDING MEDIUM)

(1) Configuration of Magnetic Recording Medium

The magnetic recording medium 110 according to the second embodiment isa long, vertical magnetic recording medium and includes a film type baselayer 111, a soft magnetic underlayer 112 (hereinafter referred to asSUL), a first seed layer 113A, a second seed layer 113B, a first groundlayer 114A, a second ground layer 114B, and a magnetic layer 115 asillustrated in FIG. 8. The SUL 112, the first and second seed layers113A and 113B, first and second ground layers 114A and 114B, and themagnetic layer 115 may be, for example, vacuum thin films such as layersformed by sputtering (hereinafter also referred to as “sputteredlayer”), or the like.

The SUL 112, the first and second seed layers 113A and 113B, and thefirst and second ground layer 114A and 114B are provided between onemain surface of the base layer 111 (hereinafter referred to as“surface”) and the magnetic layer 115, and the SUL 112, the first seedlayer 113A, the second seed layer 113B, the first ground layer 114A, andthe second ground layer 114B are stacked in this order from the baselayer 111 toward the magnetic layer 115.

The magnetic recording medium 110 may further include a protective layer116 provided on the magnetic layer 115 and a lubricating layer 117provided on the protective layer 116 as necessary. Furthermore, themagnetic recording medium 110 may further include a back layer 118provided on the other main surface (hereinafter referred to as “backsurface”) of the base layer 111 as necessary.

Hereinafter, the longitudinal direction of the magnetic recording medium110 (longitudinal direction of the base layer 111) is referred to as amachine direction (MD). Here, the machine direction refers to a relativemovement direction of a recording and reproducing head with respect tothe magnetic recording medium 110, that is, the direction in which themagnetic recording medium 110 runs at the time of recording andreproduction.

The magnetic recording medium 110 according to the second embodiment ispreferably used as a storage medium for a data archive, which isexpected to increase in demand in the future. This magnetic recordingmedium 110 may realize a surface recording density of 10 times or more,that is, a surface recording density of 50 Gb/in² or more, for example,of the current coating type magnetic recording medium for storage. In acase where a general linear recording type data cartridge is configuredusing the magnetic recording medium 110 having such a surface recordingdensity, a large capacity recording of 100 TB or more per data cartridgemay be realized.

The magnetic recording medium 110 according to the second embodiment ispreferably used in a recording and reproducing apparatus (recording andreproducing apparatus for recording and reproducing data) having aring-type recording head and a giant magnetoresistive (GMR) typereproducing head or a tunneling magnetoresistive (TMR) type reproducinghead. Furthermore, it is preferable that the magnetic recording medium110 according to the second embodiment uses a ring-type recording headas the servo signal write head. In the magnetic layer 115, for example,a data signal is vertically recorded by a ring-type recording head.Furthermore, in the magnetic layer 115, for example, a servo signal isvertically recorded by the ring-type recording head.

(2) Description of Each Layer

(Base Layer)

The description regarding the base layer 11 in the first embodiment isapplied to the base layer 111, and a description regarding the baselayer 111 is thus omitted.

(SUL)

The SUL 112 contains a soft magnetic material in an amorphous state. Thesoft magnetic material includes, for example, at least one of a Co-basedmaterial or an Fe-based material. The Co-based material includes, forexample, CoZrNb, CoZrTa, or CoZrTaNb. The Fe-based material includes,for example, FeCoB, FeCoZr, or FeCoTa.

The SUL 112 is a single-layer SUL, and is provided directly on the baselayer 111. An average thickness of the SUL 112 is preferably 10 nm ormore to 50 nm or less, and more preferably 20 nm or more and 30 nm orless.

The average thickness of the SUL 112 is obtained by the same method asthe method of measuring the average thickness of the magnetic layer 13in the first embodiment. Note that average thicknesses of layers otherthan the SUL 112, as described later (in other words, averagethicknesses of first and second seed layers 113A and 113B, first andsecond ground layers 114A and 114B, and a magnetic layer 115) are alsoobtained by the same method as the method of measuring the averagethickness of the magnetic layer 13 in the first embodiment. However, amagnification of a TEM image is appropriately adjusted according to thethickness of each layer.

(First and Second Seed Layers)

The first seed layer 113A contains an alloy containing Ti and Cr, andhas an amorphous state.

Furthermore, this alloy may further contain O (oxygen). The oxygen maybe impurity oxygen contained in a small amount in the first seed layer113A when the first seed layer 113A is formed by a film forming methodsuch as a sputtering method or the like.

Here, the “alloy” means at least one of a solid solution, a eutecticmaterial, an intermetallic compound, or the like, containing Ti and Cr.The “amorphous state” means a state in which a halo is observed by X-raydiffraction, electron beam diffraction method or the like, and a crystalstructure may not be specified.

An atomic ratio of Ti to a total amount of Ti and Cr contained in thefirst seed layer 113A is preferably 30 atomic % or more and less than100 atomic %, and more preferably 50 atomic % or more and less than 100atomic %. When the atomic ratio of Ti is less than 30 atomic %, a (100)plane of a body-centered cubic lattice (bcc) structure of Cr is aligned,so that there is a possibility that alignment of the first and secondground layers 114A and 114B formed on the first seed layer 113A will bereduced.

The atomic ratio of Ti is obtained as follows. Depth direction analysis(depth profile measurement) of the first seed layer 113A by augerelectron spectroscopy (hereinafter referred to as “AES”) is performedwhile ion-milling the magnetic recording medium 110 from the magneticlayer 115 side. Next, an average composition (average atomic ratio) ofTi and Cr in the film thickness direction is obtained from the obtaineddepth profile. Next, the atomic ratio of Ti is obtained using theobtained average composition of Ti and Cr.

In a case where the first seed layer 113A contains Ti, Cr and O, anatomic ratio of O to a total amount of Ti, Cr and O contained in thefirst seed layer 113A is preferably 15 atomic % or less, and morepreferably is 10 atomic % or less. In a case where the atomic ratio of Oexceeds 15 atomic %, TiO₂ crystals are formed, which affects nucleationof the first and second ground layers 114A and 114B formed on the firstseed layer 113A, so that there is a possibility that the alignment ofthe first and second ground layers 114A and 114B will be reduced. Theatomic ratio of O is obtained using a method similar to a method ofanalyzing the atomic ratio of Ti. The alloy contained in the first seedlayer 113A may further contain an element other than Ti and Cr as anadditional element. This additional element may be, for example, one ormore elements selected from the group including Nb, Ni, Mo, Al, and W.

The average thickness of the first seed layer 113A is preferably 2 nm to15 nm, and more preferably 3 nm to 10 m.

The second seed layer 113B contains, for example, NiW or Ta, and has acrystalline state. The average thickness of the second seed layer 113Bis preferably 3 nm to 20 nm, and more preferably 5 nm to 15 nm.

The first and second seed layers 113A and 113B have a crystal structuresimilar to that of the first and second ground layers 114A and 114B, andare not seed layers provided for the purpose of crystal growth, but areseed layers improving vertical alignment of the first and second groundlayers 114A and 114B by amorphous states of the first and second seedlayers 113A and 113B.

(First and Second Ground Layers)

It is preferable that the first and second ground layers 114A and 114Bhave a crystal structure similar as that of the magnetic layer 115. In acase where the magnetic layer 115 contains a Co-based alloy, it ispreferable that the first and second ground layers 114A and 114B containa material having a hexagonal closest-packed (hcp) structure similar tothat of the Co-based alloy and a c axis of the hcp structure is alignedin a direction (that is, film thickness direction) perpendicular to afilm surface. The reason is because the alignment of the magnetic layer115 can be improved and matching in a lattice constant between thesecond ground layer 114B and the magnetic layer 115 can be maderelatively good. As the material having the hexagonal closest-packed(hcp) structure, it is preferable to use a material containing Ru, andspecifically, it is preferable to use Ru alone or use a Ru alloy.Examples of the Ru alloy can include Ru alloy oxides such as Ru—SiO₂,Ru—TiO₂, Ru—ZrO₂, and the like, and the Ru alloy may be any one ofRu—SiO₂, Ru—TiO₂, and Ru—ZrO₂.

As described above, similar materials can be used as the materials ofthe first and second ground layers 114A and 114B. However, intendedeffects of each of the first and second ground layers 114A and 114B aredifferent from each other. Specifically, the second ground layer 114Bhas a film structure promoting a granular structure of the magneticlayer 115 which is an upper layer of the second ground layer 114B, andthe first ground layer 114A has a film structure with a high crystalalignment. In order to obtain such a film structure, it is preferablethat film forming conditions such as sputtering conditions or the likeof each of the first and second ground layers 114A and 114B are made tobe different from each other.

The average thickness of the first ground layer 114A is preferably 3 nmto 15 nm or less, and more preferably 5 nm to 10 nm. The averagethickness of the second ground layer 114B is preferably 7 nm to 40 nm,and more preferably 10 nm to 25 nm.

(Magnetic Layer)

The magnetic layer (also referred to as a recording layer) 115 may be avertical magnetic recording layer in which a magnetic material isvertically aligned. It is preferable that the magnetic layer 115 is agranular magnetic layer containing a Co-based alloy, in terms ofimprovement of a recording density. The granular magnetic layer containsferromagnetic crystal particles containing the Co-based alloy andnonmagnetic grain boundaries (nonmagnetic material) surrounding theferromagnetic crystal particles. More specifically, the granularmagnetic layer contains columns (columnar crystal) containing a Co-basedalloy and nonmagnetic grain boundaries (for example, oxides such asSiO₂) surrounding the columns and magnetically separating the respectivecolumns from each other. In this structure, the magnetic layer 115having a structure in which the respective columns are magneticallyseparated from each other may be configured.

The Co-based alloy has a hexagonal closest-packed (hcp) structure, and ac-axis of the hcp structure is aligned in the direction (film thicknessdirection) perpendicular to the film surface. As the Co-based alloy, itis preferable to use a CoCrPt-based alloy containing at least Co, Cr,and Pt. The CoCrPt-based alloy may further contain an additive element.Examples of the additive element can include one or more elementsselected from the group including Ni and Ta. The nonmagnetic grainboundaries surrounding the ferromagnetic crystal grains contain anonmagnetic metallic material. Here, the metal includes a metalloid. Asthe nonmagnetic metal material, for example, at least one of a metaloxide or a metal nitride can be used, and it is preferable to use themetal oxide, in terms of more stable maintenance of the granularstructure. Examples of the metal oxide can include metal oxidescontaining one or more elements selected from the group including Si,Cr, Co, Al, Ti, Ta, Zr, Ce, Y, Hf, and the like, and the metal oxide ispreferably a metal oxide including at least Si oxide (that is, SiO₂).Specific examples of the metal oxide can include SiO₂, Cr₂O₃, CoO,Al₂O₃, TiO₂, Ta₂O₅, ZrO₂, HfO₂, and the like. Examples of the metalnitride can include metal nitrides containing one or more elementsselected from the group including Si, Cr, Co, Al, Ti, Ta, Zr, Ce, Y, Hf,and the like. Specific examples of the metal nitride can include SiN,TiN, AlN, and the like.

It is preferable that the CoCrPt-based alloy contained in theferromagnetic crystal particle and the Si oxide contained in thenonmagnetic grain boundary have an average composition represented inthe following Formula (1). The reason is because a saturationmagnetization amount Ms in which an influence of a demagnetizing fieldcan be suppressed and a sufficient reproduction output can be obtainedcan be realized, resulting in further improvement of recording andreproduction characteristics.

(Co_(x)Pt_(y)Cr_(100-x-y))_(100-z)—(SiO₂)_(z)  (1)

(where in General Formula (1), x, y, and z are values within ranges inwhich 69≤x≤75, 10≤y≤16, and 9≤Z≤12, are satisfied, respectively).

Note that the above composition can be obtained as follows. An averagecomposition (average atomic ratio) of Co, Pt, Cr, Si, and 0 in the filmthickness direction is obtained by performing the depth directionanalysis on the magnetic layer 115 by the AES while ion-milling themagnetic recording medium 110 from the magnetic layer 115 side.

An average thickness t_(m) [nm] of the magnetic layer 115 is preferably9 nm≤t_(m)≤90 nm, more preferably 9 nm≤t_(m)≤20 nm, and still morepreferably 9 nm≤t_(m)≤15 nm. The average thickness t_(m) of the magneticlayer 13 is within the above numerical range, so that electromagneticconversion characteristics can be improved.

(Protective Layer)

The protective layer 116 contains, for example, a carbon material orsilicon dioxide (SiO₂), and it is preferable that the protective layer116 contains a carbon material in view of film strength of theprotective layer 116. Examples of the carbon material include graphite,diamond-like carbon (DLC), diamond, or the like.

(Lubricating Layer)

The lubricating layer 117 contains at least one lubricant. Thelubricating layer 117 may further contain various additives, forexample, a rust inhibitor, as necessary. A lubricant has at least twocarboxyl groups and one ester bond, and contains at least one ofcarboxylic acid-based compounds represented by the following GeneralFormula (1). The lubricant may further contain a lubricant other thanthe carboxylic acid-based compound represented by the following GeneralFormula (1).

(where, Rf is an unsubstituted or substituted saturated or unsaturatedfluorine-containing hydrocarbon group or a hydrocarbon group, Es is anester bond, R may be absent, but is an unsubstituted or substitutedsaturated or unsaturated hydrocarbon group).

It is preferable that the carboxylic acid-based compound is representedby the following General formula (2) or (3).

(where, Rf is an unsubstituted or substituted saturated or unsaturatedfluorine-containing hydrocarbon group or a hydrocarbon group).

(where, Rf is an unsubstituted or substituted saturated or unsaturatedfluorine-containing hydrocarbon group or a hydrocarbon group).

It is preferable that the lubricant contains one or both of thecarboxylic acid-based compound represented by the above General Formulas(2) and (3).

When the lubricant containing the carboxylic acid-based compoundrepresented by General Formula (1) is coated on the magnetic layer 115,the protective layer 116 or the like, a lubricating action is exhibitedby cohesion between the fluorine-containing hydrocarbon groups or thehydrocarbon groups Rf, which are hydrophobic groups. In a case where theRf group is the fluorine-containing hydrocarbon group, it is preferablethat a total carbon number is 6 to 50 and a total carbon number of afluorinated hydrocarbon group is 4 to 20. The Rf group may be, forexample, a saturated or unsaturated straight chain, branched chain, orcyclic hydrocarbon group, but may preferably be a saturated straightchain hydrocarbon group.

For example, in a case where the Rf group is the hydrocarbon group, itis preferable that the Rf group is a group represented by the followingGeneral Formula (4).

(where in General Formula (4), 1 is an integer selected from the rangeof 8 to 30, and more preferably 12 to 20).

Furthermore, in a case where the Rf group is the fluorine-containinghydrocarbon group, it is preferable that the Rf group is grouprepresented by following General formula (5).

(where in General Formula (5), m and n are, respectively, integersindependently selected from each other within the following ranges: m: 2to 20, n: 3 to 18, and more preferably m: 4 to 13, n: 3 to 10).

The fluorinated hydrocarbon group may be concentrated at one position inthe molecule as described above or may be dispersed as in the followingGeneral Formula (6), and may be —CHF₂, —CHF—, or the like, as well as—CF₃ or —CF₂—.

(where in General Formulas (5) and (6), n1+n2=n and m1+m2=m).

The reason why the number of carbon atoms in General Formulas (4), (5),and (6) is limited as described above is because when the number (1 orthe sum of m and n) of carbon atoms constituting an alkyl group or afluorine-containing alkyl group is equal to or more than the above lowerlimit, a length becomes an appropriate length, so that the cohesionbetween the hydrophobic groups is effectively exhibited and friction andwear durability is improved.

Furthermore, the reason is because when the number of carbon atoms isequal to or less than the above upper limit, solubility in a solvent ofa lubricant including the carboxylic acid-based compound is kept good.

In particular, when the Rf group in General Formulas (1), (2) and (3)contains a fluorine atom, there is an effect in reducing a frictioncoefficient and improving traveling performance. However, it ispreferable to provide a hydrocarbon group between thefluorine-containing hydrocarbon group and the ester bond to separate thefluorine-containing hydrocarbon group and the ester bond from eachother, thereby securing stability of the ester bond and preventinghydrolysis.

Furthermore, the Rf group may have a fluoroalkyl ether group or aperfluoropolyether group. An R group in General Formula (1) may beabsent, but in a case where the R group in General Formula (1) ispresent, it is preferably a hydrocarbon chain having a relatively smallnumber of carbon atoms.

Furthermore, the Rf group or R group contains one element or a pluralityof elements selected from the group including nitrogen, oxygen, sulfur,phosphorus, and halogen as constituent elements, and may further have ahydroxyl group, a carboxyl group, and a carbonyl group, an amino group,an ester bond, and the like, in addition to the functional groupdescribed above.

It is preferable that the carboxylic acid-based compound represented byGeneral Formula (1) is specifically at least one of the compounds shownbelow. In other words, it is preferable that the lubricant contains atleast one of the compounds shown below.

CF₃(CF₂)₇(CH₂)₁₀COOCH(COOH)CH₂COOH

CF₃(CF₂)₃(CH₂)₁₀COOCH(COOH)CH₂COOH

C₁₇H₃₅COOCH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₂OCOCH₂CH(C₁₈H₃₇)COOCH(COOH)CH₂COOH

CF₃(CF₂)₇COOCH(COOH)CH₂COOH

CHF₂(CF₂)₇COOCH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₂OCOCH₂CH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₆OCOCH₂CH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₁₁OCOCH₂CH(COOH)CH₂COOH

CF₃(CF₂)₃(CH₂)₆OCOCH₂CH(COOH)CH₂COOH

C₁₈H₃₇OCOCH₂CH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₄COOCH(COOH)CH₂COOH

CF₃(CF₂)₃(CH₂)₄COOCH(COOH)CH₂COOH

CF₃(CF₂)₃(CH₂)₇COOCH(COOH)CH₂COOH

CF₃(CF₂)₉(CH₂)₁₀COOCH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₁₂COOCH(COOH)CH₂COOH

CF₃(CF₂)₅(CH₂)₁₀COOCH(COOH)CH₂COOH

CF₃(CF₂)₇CH(C₉H₁₉)CH₂CH═CH(CH₂)₇COOCH(COOH)CH₂COOH

CF₃(CF₂)₇CH(C₆H₁₃)(CH₂)₇COOCH(COOH)CH₂COOH

CH₃(CH₂)₃(CH₂CH₂CH(CH₂CH₂(CF₂)₉CF₃))₂(CH₂)₇COOCH(COOH)CH₂COOH

The carboxylic acid-based compound represented by the General Formula(1) is soluble in a non-fluorinated solvent having a small load on anenvironment, and has an advantage that an operation such as coating,immersion, spraying, or the like, can be performed using ageneral-purpose solvent such as, for example, a hydrocarbon-basedsolvent, a ketone-based solvent, an alcohol-based solvent, anester-based solvent, and the like. Specifically, examples of thegeneral-purpose solvent can include hexane, heptane, octane, decane,dodecane, benzene, toluene, xylene, cyclohexane, methyl ethyl ketone,methyl isobutyl ketone, methanol, ethanol, isopropanol, diethyl ether,tetrahydrofuran, dioxane, cyclohexanone, and the like.

In a case where the protective layer 116 contains a carbon material,when the carboxylic acid-based compound is coated on the protectivelayer 116 as a lubricant, two carboxyl groups and at least one esterbond group, which are polar group parts of lubricant molecules, can beadsorbed on the protective layer 116 to form a particularly durablelubricating layer 117 by cohesion between hydrophobic groups.

Note that the lubricant is held not only on the surface of the magneticrecording medium 110 as the lubricating layer 117 as described above,but may also be contained and held in layers such as the magnetic layer115, the protective layer 116 and the like constituting the magneticrecording medium 110.

(Back Layer)

The description regarding the back layer 14 in the first embodiment isapplied to the back layer 118.

(3) Physical Properties and Structure

All of the descriptions regarding the physical properties and thestructure described in the above (3) of 2. are also applied to thesecond embodiment. For example, the average thickness t_(T), dimensionalchange amount Δw, thermal expansion coefficient α, humidity expansioncoefficient β, Poisson's ratio ρ, elastic limit value σ_(MD) in thelongitudinal direction, friction coefficient μ between the magneticsurface and the back surface, a surface roughness R_(ab) of the backlayer 118, and width deformation coefficient b of the magnetic recordingmedium 110 may be similar to those in the first embodiment. Therefore, adescription of the physical properties and the structure of the magneticrecording medium of the second embodiment is omitted.

(4) Configuration of Sputtering Apparatus

Hereinafter, an example of a configuration of a sputtering apparatus 120used for manufacturing the magnetic recording medium 110 according tothe second embodiment will be described with reference to FIG. 9. Thesputtering apparatus 120 is a continuous winding type sputtering usedfor forming the SUL 112, the first seed layer 113A, the second seedlayer 113B, the first ground layer 114A, the second ground layer 114B,and the magnetic layer 115, and includes a film forming chamber 121, adrum 122, which is a metal can (rotary body), cathodes 123 a to 123 f, asupply reel 124, a winding reel 125, and a plurality of guide rollers127 a to 127 c and 128 a to 128 c, as shown in FIG. 9. The sputteringapparatus 120 is, for example, an apparatus using a DC (direct current)magnetron sputtering manner, but the sputtering manner is not limitedthereto.

The film forming chamber 121 is connected to a vacuum pump (not shown)through an exhaust port 126, and the atmosphere in the film formingchamber 121 is set to a predetermined degree of vacuum by the vacuumpump. The drum 122 having a rotatable configuration, the supply reel124, and the winding reel 125 are arranged in the film forming chamber121. The plurality of guide rollers 127 a to 127 c for guidingconveyance of the base layer 111 between the supply reel 124 and thedrum 122 and the plurality of guide rollers 128 a to 128 c for guidingconveyance of the base layer 111 between the drum 122 and the windingreel 125 are provided in the film forming chamber 121. At the time ofsputtering, the base layer 111 unwound from the supply reel 124 is woundaround the winding reel 125 through the guide rollers 127 a to 127 c,the drum 122, and the guide rollers 128 a to 128 c. The drum 122 has acylindrical shape, and the long base layer 111 is conveyed along acircumferential surface of the cylindrical surface of the drum 122. Thedrum 122 is provided with a cooling mechanism (not shown), and is cooledto, for example, about −20° C. at the time of the sputtering. Aplurality of cathodes 123 a to 123 f is arranged in the film formingchamber 121 so as to face the circumferential surface of the drum 122Target are set on the cathodes 123 a to 123 f, respectively.Specifically, targets for forming the SUL 112, the first seed layer113A, the second seed layer 113B, the first ground layer 114A, thesecond ground layer 114B, and the magnetic layer 115 are set on thecathodes 123 a, 123 b, 123 c, 123 d, 123 e, and 123 f, respectively. Aplurality of types of films, that is, the SUL 112, the first seed layer113A, the second seed layer 113B, the first ground layer 114A, thesecond ground layer 114B, and the magnetic layer 115 are simultaneouslyformed by these cathodes 123 a to 123 f.

In the sputtering apparatus 120 having the configuration describedabove, the SUL 112, the first seed layer 113A, the second seed layer113B, the first ground layer 114A, the second ground layer 114B, and themagnetic layer 115 are continuously formed by a RolltoRoll method.

(5) Method of Manufacturing Magnetic Recording Medium

The magnetic recording medium 110 according to the second embodiment canbe manufactured, for example, as follows.

First, the SUL 112, the first seed layer 113A, the second seed layer113B, the first ground layer 114A, the second ground layer 114B, and themagnetic layer 115 are sequentially formed on a surface of the baselayer 111 using the sputtering apparatus 120 shown in FIG. 9.Specifically, the films are formed as follows. First, the film formingchamber 121 is evacuated to a predetermined pressure. Thereafter, thetargets set on the cathodes 123 a to 123 f are sputtered while a processgas such as an Ar gas or the like is introduced into the film formingchamber 121 Therefore, the SUL 112, the first seed layer 113A, thesecond seed layer 113B, the first ground layer 114A, the second groundlayer 114B, and the magnetic layer 115 are sequentially formed on thesurface of the traveling base layer 111.

The atmosphere of the film forming chamber 121 at the time of thesputtering is set to, for example, about 1×10⁻⁵ Pa to 5×10⁻⁵ Pa. Filmthicknesses and characteristics of the SUL 112, the first seed layer113A, the second seed layer 113B, the first ground layer 114A, thesecond ground layer 114B, and the magnetic layer 115 can be controlledby adjusting a tape line speed at which the base layer 111 is wound, apressure (sputtering gas pressure) of the process gas such as the Ar gasor the like introduced at the time of the sputtering, supplied power,and the like.

Next, the protective layer 116 is formed on the magnetic layer 115. As amethod of forming the protective layer 116, for example, a chemicalvapor deposition (CVD) method or a physical vapor deposition (PVD)method can be used.

Next, a binder, inorganic particles, a lubricant, and the like arekneaded and dispersed in a solvent to prepare a coating material forforming a back layer. Next, the back layer 118 is formed on the backsurface of the base layer 111 by applying the coating material forforming a back layer on the back surface of the base layer 111 and thendrying the coating material.

Next, for example, the lubricant is coated on the protective layer 116to form the lubricating layer 117. As a method of coating the lubricant,for example, various coating methods such as gravure coating, dipcoating and the like can be used. Next, the magnetic recording medium110 is cut into a predetermined width, as necessary. Thus, the magneticrecording medium 110 shown in FIG. 8 is obtained.

(6) Effect

In the magnetic recording medium 110 according to the second embodiment,similar to the first embodiment, a change in width of the magneticrecording medium 110 may be suppressed by adjusting tension of themagnetic recording medium 110 in the longitudinal direction by therecording and reproducing apparatus. For example, even if there is achange in temperature and humidity that may cause a change in the widthof the magnetic recording medium 110, the width of the magneticrecording medium 110 can be kept constant or substantially constant. Thechange in width by the tension adjustment may be suppressed even afterlong-term storage.

Moreover, although the magnetic recording medium 110 is as thin ast_(T)≤5.6 μm, the magnetic recording medium 110 is excellent in handlingproperties.

(7) Modification

The magnetic recording medium 110 may further include an ground layerbetween the base layer 111 and the SUL 112. Since the SUL 112 has theamorphous state, the SUL 112 does not play a role of promoting epitaxialgrowth of a layer formed on the SUL 112, but is desired not to disturbthe crystal alignment of the first and second ground layers 114A and114B formed on the SUL 112. For this purpose, it is preferable that thesoft magnetic material has a fine structure that does not form a column,but in a case where an influence of the release of a gas such asmoisture or the like from the base layer 111 is large, the soft magneticmaterial may be coarsened to disturb the crystal alignment of the firstand second ground layers 114A and 114B formed on the SUL 112. In orderto suppress the influence of the release of the gas such as moisture orthe like from the base layer 111, it is preferable that the ground layercontaining an alloy containing Ti and Cr and an having amorphous stateis provided between the base layer 111 and the SUL 112, as describedabove. As a specific configuration of the ground layer, a configurationsimilar to that of the first seed layer 113A of the second embodimentcan be adopted.

The magnetic recording medium 110 may not include at least one of thesecond seed layer 113B or the second ground layer 114B. However, it ismore preferable that the magnetic recording medium 110 includes both ofthe second seed layer 113B and the second base layer 114B, in terms ofimprovement a SNR.

The magnetic recording medium 110 may include an antiparallel coupledSUL (APC-SUL) instead of the single-layer SUL.

4. THIRD EMBODIMENT (EXAMPLE OF VACUUM THIN FILM TYPE MAGNETIC RECORDINGMEDIUM)

(Configuration of Magnetic Recording Medium)

As shown in FIG. 10, the magnetic recording medium 130 according to athird embodiment includes a base layer 111, an SUL 112, a seed layer131, a first ground layer 132A, a second ground layer 132B, and amagnetic layer 115. Note that, in the third embodiment, the same partsas those in the second embodiment are indicated by the same referencenumerals and a description thereof will be omitted.

The SUL 112, the seed layer 131, and the first and second ground layers132A and 132B are provided between one main surface of the base layer111 and the magnetic layer 115, and the SUL 112, the seed layer 131, thefirst ground layer 132A, and the second ground layer 132B aresequentially stacked from the base layer 111 toward the magnetic layer115.

(Seed Layer)

The seed layer 131 contains Cr, Ni, and Fe, and has a face-centeredcubic lattice (fcc) structure, and a (111) plane of the face-centeredcubic lattice structure is preferentially aligned so as to be parallelwith a surface of the base layer 111. Here, the preferential alignmentmeans a state in which a diffraction peak intensity from the (111) planeof the face-centered cubic lattice structure is larger than diffractionpeaks from other crystal planes in a θ-2θ scan of an X-ray diffractionmethod or a state in which only the diffraction peak intensity from the(111) plane of the face-centered cubic lattice structure is observed inthe θ-2θ scan of the X-ray diffraction method.

An intensity ratio of X-ray diffraction of the seed layer 131 ispreferably 60 cps/nm or more, more preferably 70 cps/nm or more, andstill more preferably 80 cps/nm or more, in terms of improvement of theSNR. Here, the intensity ratio of the X-ray diffraction of the seedlayer 131 is a value (I/D)(cps/nm)) obtained by dividing an intensityI(cps) of the X-ray diffraction of the seed layer 131 by an averagethickness D (nm) of the seed layer 131.

It is preferable that Cr, Ni, and Fe contained in the seed layer 131have an average composition represented by the following Formula (2).

Cr_(X)(Ni_(Y)Fe_(100-Y))_(100-X)  (2)

(where in Formula (2), X is in the range in which 10≤X≤45 is satisfied,Y is in the range in which 60≤Y≤90 is satisfied). When X is in the aboverange, (111) alignment of a face-centered cubic lattice structure of Cr,Ni, and Fe is improved, so that a better SNR can be obtained. Similarly,when Y is in the above range, the (111) alignment of the face-centeredcubic lattice structure of Cr, Ni, and Fe is improved, so that a betterSNR can be obtained.

It is preferable that the average thickness of the seed layer 131 is 5nm or more to 40 nm or less. By setting the average thickness of theseed layer 131 to be in this range, the (111) alignment of theface-centered cubic lattice structure of Cr, Ni, and Fe is improved, sothat a better SNR can be obtained. Note that the average thickness ofthe seed layer 131 is obtained in a manner similar to that of themagnetic layer 13 in the first embodiment. However, a magnification of aTEM image is appropriately adjusted according to the thickness of theseed layer 131.

(First and Second Ground Layers)

The first ground layer 132A contains Co and O having a face-centeredcubic lattice structure, and has a column (columnar crystal) structure.In the first ground layer 132A containing Co and O, substantially aneffect (function) substantially similar to that of the second groundlayer 132B containing Ru is obtained. A concentration ratio of anaverage atomic concentration of O to an average atomic concentration ofCo ((average atomic concentration of O)/(average atomic concentration ofCo)) is 1 or more. When the concentration ratio is 1 or more, the effectof providing the first base layer 132A is improved, so that a better SNRcan be obtained. It is preferable that the column structure is inclinedin terms of improvement of the SNR. It is preferable that a direction ofthe inclination is a longitudinal direction of the long-shaped magneticrecording medium 130. The reason why it is preferable that the directionof the inclination is the longitudinal direction is as follows. Themagnetic recording medium 130 according to the present embodiment is aso-called magnetic recording medium for linear recording, and arecording track is parallel with the longitudinal direction of themagnetic recording medium 130. Furthermore, the magnetic recordingmedium 130 according to the present embodiment is also a so-calledperpendicular magnetic recording medium, and it is preferable that acrystal alignment axis of the magnetic layer 115 is perpendicular interms of recording characteristics, but an inclination may be generatedin the crystal alignment axis of the magnetic layer 115 due to aninfluence of an inclination of the column structure of the first groundlayer 132A. In the magnetic recording medium 130 for linear recording,in a relationship with the head magnetic field at the time of recording,the influence of the inclination of the crystal alignment axis on therecording characteristics can be reduced in a configuration in which thecrystal alignment axis of the magnetic layer 115 is inclined in thelongitudinal direction of the magnetic recording medium 130 as comparedwith a configuration in which the crystal alignment axis of the magneticlayer 115 is inclined in the width direction of the magnetic recordingmedium 130. In order to incline the crystal alignment axis of themagnetic layer 115 in the longitudinal direction of the magneticrecording medium 130, it is preferable that the inclination direction ofthe column structure of the first ground layer 132A is the longitudinaldirection of the magnetic recording medium 130 as described above.

It is preferable that the inclination angle of the column structure islarger than 0° and is 60° or less. In the range in which the inclinationangle is large than 0° and is 60° or less, a change in a tip shape ofthe column contained in the first ground layer 132A is large, so thatthe tip shape becomes substantially a triangular shape. Therefore, aneffect of the granular structure tends to be improved, noise tends to bereduced, and the SNR tends to be improved. On the other hand, when theinclination angle exceeds 60°, the change in the tip shape of the columncontained in the first foundation layer 132A is small, so that it isdifficult for the tip shape to become substantially a triangular shape.Therefore, a noise reduction effect tends to be degraded. An averageparticle diameter of the column structure is 3 nm or more to 13 nm orless. When the average particle size is less than 3 nm, the averageparticle size of the column structure included in the magnetic layer 115is reduced, and thus, there is a possibility that an ability to hold arecord with a current magnetic material will be deteriorated. On theother hand, when the average particle size is 13 nm or less, the noiseis suppressed, so that a better SNR can be obtained.

An average thickness of the first ground layer 132A is preferably 10 nmor more to 150 nm or less. When the average thickness of the firstground layer 132A is 10 nm or more, (111) alignment of the face-centeredcubic lattice structure of the first ground layer 132A is improved, sothat a better SNR can be obtained. On the other hand, when the averagethickness of the first ground layer 132A is 150 nm or less, an increasein a particle diameter of the column can be suppressed. Therefore, thenoise is suppressed, so that a better SNR can be obtained. Note that theaverage thickness of the first ground layer 132A is obtained in a mannersimilar to the magnetic layer 13 in the first embodiment. However, amagnification of an TEM image is appropriately adjusted according to thethickness of the first ground layer 132A.

It is preferable that the second ground layer 132B has a crystalstructure similar to that of the magnetic layer 115. In a case where themagnetic layer 115 contains a Co-based alloy, the second ground layer132B contains a material having a hexagonal closest-packed (hcp)structure similar to that of the Co-based alloy, and it is preferablethat a c-axis of the hcp structure is aligned in a direction (that is, afilm thickness direction) perpendicular to a film surface. The reason isbecause alignment of the magnetic layer 115 can be improved and matchingin a lattice constant between the second ground layer 132B and themagnetic layer 115 can be made relatively good. As the material havingthe hexagonal closest-packed structure, it is preferable to use amaterial containing Ru, and specifically, it is preferable to use Rualone or use a Ru alloy. Examples of the Ru alloy can include an Rualloy oxide such as Ru—SiO₂, Ru—TiO₂, Ru—ZrO₂, or the like.

An average thickness of the second ground layer 132B may be thinner thanthat of an ground layer (for example, an ground layer containing Ru) ina general magnetic recording medium, and can be, for example, 1 nm ormore to 5 nm or less. Since the seed layer 131 and the first groundlayer 132A having the configurations described above are provided underthe second ground layer 132B, even though the average thickness of thesecond ground layer 132B is thin as described above, a good SNR isobtained. Note that the average thickness of the second ground layer132B is obtained in a manner similar to the magnetic layer 13 in thefirst embodiment.

However, a magnification of an TEM image is appropriately adjustedaccording to the thickness of the second ground layer 132B.

(Effect)

In the magnetic recording medium 130 according to the third embodiment,as in the first embodiment, a width of the magnetic recording medium 10can be kept constant or substantially constant by adjusting tension ofthe magnetic recording medium 10 in the longitudinal direction. Themagnetic recording medium 130 according to the third embodiment includesthe seed layer 131 and the first ground layer 132A between the baselayer 111 and the second ground layer 132B. The seed layer 131 containsCr, Ni, and Fe, and has a face-centered cubic lattice structure, and a(111) plane of the face-centered cubic structure is preferentiallyaligned so as to be parallel with a surface of the base layer 111. Thefirst ground layer 132A has a column structure in which it contains Coand O, a ratio of an average atomic concentration of O to an averageatomic concentration of Co is 1 or more, and an average particlediameter is 3 nm or more to 13 nm or less. Therefore, it is possible torealize the magnetic layer 115 having a good crystal alignment and ahigh coercive force without using Ru, which is an expensive material, asthin as possible by reducing the thickness of the second ground layer132B.

Ru contained in the second ground layer 132B has the same hexagonalclosest-packed lattice structure as that of Co, which is a maincomponent of the magnetic layer 115. Therefore, Ru has an effect ofimproving the crystal alignment of the magnetic layer 115 and promotinga granular property. Furthermore, in order to further improve thecrystal alignment of Ru contained in the second ground layer 132B, thefirst ground layer 132A and the seed layer 131 are provided under thesecond ground layer 132B. In the magnetic recording medium 130 accordingto the third embodiment, an effect (function) substantially similar tothat of the second ground layer 132B containing Ru is realized by thefirst ground layer 132A containing cheap CoO having the face-centeredcubic lattice structure. Therefore, the thickness of the second groundlayer 132B can be reduced. Furthermore, in order to improve the crystalalignment of the first ground layer 132A, the seed layer 131 containingCr, Ni, and Fe is provided.

5. EXAMPLE

Hereinafter, the present technology will be specifically described byExamples, but the present technology is not limited to only theseExamples.

In the following examples and comparative examples, an average thicknesst_(T) of the magnetic tape, a dimensional change amount Δw of themagnetic tape in the width direction with respect to a change in tensionof the magnetic tape in the longitudinal direction, a thermal expansioncoefficient α of the magnetic tape, a humidity expansion coefficient βof the magnetic tape, Poisson's ratio ρ of magnetic tape, an elasticlimit value σ_(MD) of the magnetic tape in the longitudinal direction,an average thickness t_(m) of the magnetic layer, a squareness ratio S2,an average thickness to of the back layer, a surface roughness R_(ab) ofthe back layer, and an interlayer friction coefficient μ between themagnetic surface and the back surface are values obtained by themeasurement method described above in the first embodiment. However, asdescribed later, in Example 11, a speed V at the time of measuring anelastic limit value σ_(MD) in a longitudinal direction was set to avalue different from the measurement method described in the firstembodiment.

Example 1

(Process of Preparing Magnetic Layer-Forming Coating Material)

A magnetic layer-forming coating material was prepared as follows.First, a first composition of the following mixture was kneaded with anextruder. Next, the kneaded first composition and a second compositionof the following mixture were added to a stirring tank equipped with adisperser and preliminary mixing was carried out. Subsequently, sandmill mixing was performed again and subjected to filtering to prepare amagnetic layer-forming coating material.

(First Composition)

Powder of ε iron oxide nanoparticles (ε-Fe₂O₃ crystal particles): 100parts by mass Vinyl chloride resin (30 mass % of a cyclohexanonesolution): 10 parts by mass (containing a polymerization degree of 300,Mn=10000, OSO₃K=0.07 mmol/g as a polar group, and secondary OH=0.3mmol/g)

Aluminum oxide powder: 5 parts by mass

(α-Al₂O₃, average particle size 0.2 μm)

Carbon black: 2 parts by mass

(Manufactured by TOKAI CARBON CO., LTD, trade name: SEAST TA)

(Second Composition)

Vinyl chloride resin: 1.1 parts by mass

(Resin solution: 30% by mass of resin, 70% by mass of cyclohexanone)

n-Butyl stearate: 2 parts by mass

Methyl ethyl ketone: 121.3 parts by mass

Toluene: 121.3 parts by mass

Cyclohexanone: 60.7 parts by mass

Finally, 4 parts by mass of polyisocyanate (trade name: Coronate L,manufactured by Nippon Polyurethane Co., Ltd.) and 2 parts by mass ofmyristic acid were added as a curing agent to the magnetic layer-formingcoating material prepared as described above.

(Process of Preparing Ground Layer-Forming Coating Material)

A ground layer-forming coating material was prepared as follows. First,a third composition of the following mixture was kneaded by an extruder.Next, the kneaded third composition and a fourth composition of thefollowing mixture were added to a stirring tank equipped with a disperand preliminary mixing was carried out. Subsequently, sand mill mixingwas further performed and the mixture was subjected to filtering toprepare a ground layer-forming coating material.

(Third Composition)

Needle-like iron oxide powder: 100 parts by mass

(α-Fe₂O₃, average major axis length 0.15 μm)

Vinyl chloride resin: 55.6 parts by mass

(Resin solution: 30% by mass of resin, 70% by mass of cyclohexanone)

Carbon black: 10 parts by mass

(Average particle size 20 nm)

(Fourth Composition)

Polyurethane resin UR8200(manufactured by TOYO BOSEKI): 18.5 parts bymass

n-Butyl stearate: 2 parts by mass

Methyl ethyl ketone: 108.2 parts by mass

Toluene: 108.2 parts by mass

Cyclohexanone: 18.5 parts by mass

Finally, 4 parts by mass of polyisocyanate (trade name: Coronate L,manufactured by Nippon Polyurethane Co., Ltd.) and 2 parts by mass ofmyristic acid were added as a curing agent to the ground layer-formingcoating material prepared as described above.

(Process of Preparing Back Layer-Forming Coating Material)

A back layer-forming coating material was prepared as follows. Thefollowing raw materials were mixed in a stirring tank equipped with adisper and subjected to filtering to prepare a back layer-formingcoating material.

Carbon black (manufactured by Asahi Carbon Co., Ltd., trade name: #80):100 parts by mass

Polyester polyurethane: 100 parts by mass

(Nippon Polyurethane Co., Ltd., trade name: N-2304)

Methyl ethyl ketone: 500 parts by mass

Toluene: 400 parts by mass

Cyclohexanone: 100 parts by mass

(Film Formation Process)

Using the coating material prepared as described above, a ground layerhaving an average thickness of 1.0 μm and a magnetic layer having anaverage thickness t_(m) of 90 nm were formed on a long polyethylenenaphthalate film (hereinafter referred to as “PEN film”) which is anonmagnetic support in the following manner. First, the groundlayer-forming coating material was applied to the film and dried to forma ground layer on the film. Next, a magnetic layer-forming coatingmaterial was applied to the ground layer and dried to form a magneticlayer on the ground layer. Note that, when the magnetic layer-formingcoating material was dried, the magnetic powder was magnetically alignedin a thickness direction of the film by a solenoid coil. Furthermore,the squareness ratio S2 in the thickness direction (vertical direction)of the magnetic tape was set to 65% by adjusting an application time ofthe magnetic field to the magnetic layer-forming coating material.

Subsequently, a back layer having an average thickness to of 0.6 μm wasapplied to the film, on which the ground layer and the magnetic layerwere formed, and dried. Then, the film, on which the ground layer, themagnetic layer, and the back layer were formed, was subjected to acuring treatment. Subsequently, calendering was performed to smooth thesurface of the magnetic layer. Here, conditions (temperature) forcalendering were adjusted so that an interlayer friction coefficient μof a magnetic surface and a back surface is about 0.5 and re-curing wassubsequently performed to obtain a magnetic tape having an averagethickness t_(T) of 5.5 μm.

(Cutting Process)

The magnetic tape obtained as described above was cut into a ½ inch(12.65 mm) width and wound around a core to obtain a pancake.

The magnetic tape obtained as described above had the characteristicsshown in Table 1. For example, a dimensional change amount Δw of themagnetic tape was 707 ppm/N.

The ½ inch-wide magnetic tape was wound around a reel prepared in thecartridge case to obtain a magnetic recording cartridge. A servo signalwas recorded on the magnetic tape. The servo signal includes a series ofinverted V-shaped magnetic patterns, and the magnetic patterns arepre-recorded in parallel in the longitudinal direction at two or morelines at known intervals (hereinafter referred to as “standard servotrack width”).

Example 2

A magnetic tape was obtained in the same manner as in Example 1 exceptthat the thickness of the PEN film was made thinner than in Example 1 sothat the dimensional change amount Δw was 750 ppm/N. The averagethickness t_(T) of the magnetic tape was 5μm. As in Example 1, amagnetic recording cartridge was manufactured using the magnetic tapeand a servo signal was then recorded on the magnetic tape.

Example 3

A magnetic tape was obtained in the same manner as in Example 1 exceptthat the thickness of the PEN film was thinner than Example 1 and theaverage thickness of the back layer and the ground layer was thinner sothat the dimensional change amount Δw was 800 ppm/N. The averagethickness t_(T) of the magnetic tape was 4.5 um. As in Example 1, amagnetic recording cartridge was manufactured using the magnetic tapeand a servo signal was then recorded on the magnetic tape.

Example 4

A magnetic tape was obtained in the same manner as in Example 1 exceptthat the thickness of the PEN film was thinner than Example 1, theaverage thickness of the back layer and the ground layer was thinner,and the curing treatment conditions of the film on which the groundlayer, the magnetic layer, and the back layer were formed were adjustedso that the dimensional change amount Δw was 800 ppm/N. As in Example 1,a magnetic recording cartridge was manufactured using the magnetic tapeand a servo signal was then recorded on the magnetic tape.

Example 5

A magnetic tape was obtained in the same manner as in Example 4 exceptthat the composition of the ground layer-forming coating material waschanged so that the thermal expansion coefficient α was 8.0 ppm/° C. Asin Example 1, a magnetic recording cartridge was manufactured using themagnetic tape and a servo signal was then recorded on the magnetic tape.

Example 6

A magnetic tape was obtained in the same manner as in Example 4 exceptthat a thin barrier layer was formed on one side of the PEN film so thatthe humidity expansion coefficient β was 3.0 ppm/% RH. As in Example 1,a magnetic recording cartridge was manufactured using the magnetic tapeand a servo signal was then recorded on the magnetic tape.

Example 7

A magnetic tape was obtained in the same manner as in Example 4 exceptthat longitudinal and transverse stretching strengths of the base filmwere changed so that the Poisson's ratio ρ was 0.31. As in Example 1, amagnetic recording cartridge was manufactured using the magnetic tapeand a servo signal was then recorded on the magnetic tape.

Example 8

A magnetic tape was obtained in the same manner as in Example 4 exceptthat the longitudinal and transverse stretching strengths of the basefilm were changed so that the Poisson's ratio ρ was 0.35. As in Example1, a magnetic recording cartridge was manufactured using the magnetictape and a servo signal was then recorded on the magnetic tape.

Example 9

A magnetic tape was obtained in the same manner as in Example 7 exceptthat the curing conditions of the film on which the ground layer, themagnetic layer, and the back layer were formed were adjusted so that theelastic limit value σ_(MD) in the longitudinal direction was 0.8 N. Asin Example 1, a magnetic recording cartridge was manufactured using themagnetic tape and a servo signal was then recorded on the magnetic tape.

Example 10

A magnetic tape was obtained in the same manner as in Example 7 exceptthat the curing conditions and re-curing conditions of the film on whichthe ground layer, the magnetic layer, and back layer were formed wereadjusted so that the elastic limit value σ_(MD) in the longitudinaldirection was 3.5 N. As in Example 1, a magnetic recording cartridge wasmanufactured using the magnetic tape and a servo signal was thenrecorded on the magnetic tape.

Example 11

A magnetic tape was obtained in a manner similar to that of Example 9.Then, the elastic limit value σ_(MD) of the obtained magnetic tape wasmeasured by changing the speed V when measuring the elastic limit valueσ_(MD) in the longitudinal direction to 5 mm/min. As a result, theelastic limit value σ_(MD) in the longitudinal direction was 0.8,without any change as compared with the elastic limit value σ_(MD) inthe longitudinal direction at a speed V of 0.5 mm/min (Example 9).

As in Example 1, a magnetic recording cartridge was manufactured usingthe magnetic tape and a servo signal was then recorded on the magnetictape.

Example 12

A magnetic tape was obtained in the same manner as in Example 7 exceptthat a coating thickness of the magnetic layer-forming coating materialwas changed so that the average thickness t_(m) of the magnetic layerwas 40 nm. As in Example 1, a magnetic recording cartridge wasmanufactured using the magnetic tape and a servo signal was thenrecorded on the magnetic tape.

Example 13

(Film Formation Process of SUL)

First, a CoZrNb layer (SUL) having an average thickness of 10 nm wasformed on a surface of a long polymer film as a nonmagnetic supportunder the following film formation conditions.

Note that a PEN film was used as the polymer film.

Film formation method: DC magnetron sputtering method

Target: CoZrNb target

Gas type: Ar

Gas pressure: 0.1 Pa

(Process of Forming First Seed Layer)

Next, a TiCr layer (first seed layer) having an average thickness of 5nm was formed on the CoZrNb layer under the following film formationconditions.

Sputtering method: DC magnetron sputtering method

Target: TiCr target

Achieved vacuum: 5 x10⁻⁵ Pa

Gas type: Ar

Gas pressure: 0.5 Pa

(Process of Forming Second Seed Layer)

Next, a NiW layer (second seed layer) having an average thickness of 10nm was formed on the TiCr layer under the following film formationconditions.

Sputtering method: DC magnetron sputtering method

Target: NiW target

Achieved vacuum: 5×10⁻⁵ Pa

Gas type: Ar

Gas pressure: 0.5 Pa

(Process of Forming First Ground Layer)

Next, a Ru layer (first ground layer) having an average thickness of 10nm was formed on the NiW layer under the following film formationconditions.

Sputtering method: DC magnetron sputtering method

Target: Ru target

Gas type: Ar

Gas pressure: 0.5 Pa

(Process of Forming Second Ground Layer)

Next, a Ru layer (second ground layer) having an average thickness of 20nm was formed on the Ru layer under the following film formationconditions.

Sputtering method: DC magnetron sputtering method

Target: Ru target

Gas type: Ar

Gas pressure: 1.5 Pa

(Process of Forming Magnetic Layer)

Next, a (CoCrPt)—(SiO₂) layer (magnetic layer) having an averagethickness of 9 nm was formed on the Ru layer under the following filmformation conditions.

Film formation method: DC magnetron sputtering method

Target: (CoCrPt)—(SiO₂)target

Gas type: Ar

Gas pressure: 1.5 Pa

(Process of Forming Protective Layer)

Next, a carbon layer (protective layer) having an average thickness of 5nm was formed on the magnetic layer under the following film formationconditions.

Film formation method: DC magnetron sputtering method

Target: carbon target

Gas type: Ar

Gas pressure: 1.0 Pa

(Process of Forming Lubricating Layer)

Next, a lubricant was applied to the protective layer to form alubricating layer.

(Process of Forming Back Layer)

Next, a back layer-forming coating material was applied to a surfaceopposite to the magnetic layer and dried to form a back layer having anaverage thickness to of 0.3 As a result, a magnetic tape having anaverage thickness t_(T) of 4.0 μm was obtained.

(Cutting Process)

The magnetic tape obtained as described above was cut into a ½ inch(12.65 mm) width.

The magnetic tape obtained as described above had the characteristicsshown in Table 1. For example, the dimensional change amount ΔW of themagnetic tape was 800 ppm/N. As in Example 1, a magnetic recordingcartridge was manufactured using the magnetic tape and a servo signalwas then recorded on the magnetic tape.

Example 14

A magnetic tape was obtained in the same manner as in Example 7 exceptthat the thickness of the back layer was changed to 0.2 μm. An averagethickness of the magnetic tape was 4.4 μm. As in Example 1, a magneticrecording cartridge was manufactured using the magnetic tape and a servosignal was then recorded on the magnetic tape.

Example 15

A magnetic tape was obtained in the same manner as in Example 7 exceptthat the composition of the back layer-forming coating material waschanged so that the surface roughness R_(ab) of the back layer was 3 nm.As in Example 1, a magnetic recording cartridge was manufactured usingthe magnetic tape and a servo signal was then recorded on the magnetictape.

Example 16

A magnetic tape was obtained in the same manner as in Example 7 exceptthat the conditions (temperature) of calendering were adjusted so thatthe friction coefficient μ was 0.20. As in Example 1, a magneticrecording cartridge was manufactured using the magnetic tape and a servosignal was then recorded on the magnetic tape.

Example 17

A magnetic tape was obtained in the same manner as in Example 7 exceptthat the composition of the back layer-forming coating material waschanged so that the surface roughness R_(ab) of the back layer was 3 nmand the conditions (temperature) of the calendering were adjusted sothat the friction coefficient μ was 0.80. As in Example 1, a magneticrecording cartridge was manufactured using the magnetic tape and a servosignal was then recorded on the magnetic tape.

Example 18

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the coating thickness of the magnetic layer-forming coatingmaterial was changed so that the average thickness t_(m) of the magneticlayer was 110 nm. As in Example 1, a magnetic recording cartridge wasmanufactured using the magnetic tape and a servo signal was thenrecorded on the magnetic tape.

Example 19

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the composition of the back layer-forming coating material waschanged so that the surface roughness R_(ab) of the back layer was 7 nm.As in Example 1, a magnetic recording cartridge was manufactured usingthe magnetic tape and a servo signal was then recorded on the magnetictape.

Example 20

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the conditions (temperature) for calendering were adjusted so thatthe friction coefficient μ was 0.18. As in Example 1, a magneticrecording cartridge was manufactured using the magnetic tape and a servosignal was then recorded on the magnetic tape.

Example 21

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the conditions (temperature) for calendering were adjusted so thatthe friction coefficient μ was 0.82. As in Example 1, a magneticrecording cartridge was manufactured using the magnetic tape and a servosignal was then recorded on the magnetic tape.

Example 22

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the squareness ratio S2 in the thickness direction (verticaldirection) of the magnetic tape was set to 73% by adjusting theapplication time of the magnetic field to the magnetic layer-formingcoating material. As in Example 1, a magnetic recording cartridge wasmanufactured using the magnetic tape and a servo signal was thenrecorded on the magnetic tape.

Example 23

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the squareness ratio S2 in the thickness direction (verticaldirection) of the magnetic tape was set to 80% by adjusting theapplication time of the magnetic field to the magnetic layer-formingcoating material. As in Example 1, a magnetic recording cartridge wasmanufactured using the magnetic tape and a servo signal was thenrecorded on the magnetic tape.

Example 24

A magnetic tape was obtained in the same manner as in Example 7 exceptthat the curing conditions and re-curing conditions of the film on whichthe ground layer, the magnetic layer, and the back layer were formedwere adjusted so that the elastic limit value σ_(MD) in the longitudinaldirection was 5.0 N. As in Example 1, a magnetic recording cartridge wasmanufactured using the magnetic tape and a servo signal was thenrecorded on the magnetic tape.

Example 25

A magnetic tape was obtained in the same manner as in Example 7, exceptthat barium ferrite (BaFe₁₂O₁₉) nanoparticles were used instead of εiron oxide nanoparticles. As in Example 1, a magnetic recordingcartridge was manufactured using the magnetic tape and a servo signalwas then recorded on the magnetic tape.

Comparative Example 1

A magnetic tape was obtained in the same manner as in Example 1 exceptthat the stretching treatment of the PEN film was changed so that thedimensional change amount Δw was 650 [ppm/N] and the winding tension inthe coating process was increased. As in Example 1, a magnetic recordingcartridge was manufactured using the magnetic tape and a servo signalwas then recorded on the magnetic tape.

Comparative Example 2

A magnetic tape was obtained in the same manner as in Example 3, exceptthat a thick base film was used and tension was increased in the dryingprocess. As in Example 1, a magnetic recording cartridge wasmanufactured using the magnetic tape and a servo signal was thenrecorded on the magnetic tape.

Comparative Example 3

A magnetic tape was obtained in the same manner as in Example 3, exceptthat a thick base film was used, a servo signal was recorded, whileadjusting tension, and tension was increased in the drying process. Asin Example 1, a magnetic recording cartridge was manufactured using themagnetic tape and a servo signal was then recorded on the magnetic tape.

Comparative Example 4

A magnetic tape was obtained in the same manner as in Example 7 exceptthat vertical alignment was not performed. As in Example 1, a magneticrecording cartridge was manufactured using the magnetic tape and a servosignal was then recorded on the magnetic tape.

(Calculation of Width Deformation Coefficient b and RunningDetermination After 10 years of Storage)

The width deformation coefficient b was obtained by the measurementmethod described in the first embodiment. Specifically, it is asfollows.

On the magnetic tape included in each of the magnetic recordingcartridges of Examples 1 to 25 and Comparative Examples 1 to 4, two ormore rows of inverted V-shaped magnetic patterns are previously recordedin parallel in the longitudinal direction at a known interval (“standardservo track width”). Each magnetic recording tape was run to be drawninto the magnetic recording and reproducing apparatus (in the forwarddirection). At the time of the drive running, two servo trackssandwiching the second data band therebetween from the top of themagnetic recording tape were reproduced and the reproduced waveformswere obtained by a digital oscilloscope (WAVEPRO 960 manufactured byLecroy Corporation). A time between the timing signals was obtained fromthe waveforms obtained from the reproduction of each servo track, adistance L1 between a leading magnetic stripe of burst A of the servotrack on the upper side of the data band and a leading magnetic stripeof burst B and a distance L2 between a leading magnetic stripe of burstA of the servo track on a lower side of the data band and a leadingmagnetic stripe of burst B are calculated, and a deviation amount of theservo track widths were obtained using the follow formula.

(Deviation amount of servo track width)={(L1−L2)/2}×tan(90°−θ1)

In this formula, L1 and L2 are the distances L1 and L2 described above,and θ1 was obtained by developing the magnetic recording tape taken outfrom the cartridge with a Ferricolloid developer and using a universaltool microscope (TOPCON TUM-220ES) and a data processing apparatus(TOPCON CA-1B).

The magnetic recording tape was stored under an environment of 32° C.and 55% for 300 hours, and a deviation amount of the servo track widthwas measured at an interval of about every 50 m over the entire lengthof a range excluding 20 m from the outer side and inner side of thewinding of the magnetic recording tape at an interval of 50 hours duringthe storage for 300 hours.

A deviation amount of the servo track width at each position of themagnetic recording tape stored for 50 hours under the environment of 32°C. and 55% was used as a reference value.

Thereafter, regarding each position, a change amount (long-term storagewidth change amount Y) of the above-mentioned deviation of the servotrack width from the reference value at each measurement time wasobtained. From the relationship between the long-term storage widthchange amount Y and the storage time, the width deformation coefficientb was obtained by using the least-squares method and defining thelong-term storage width change amount Y as Y=blog (t).

The long-term storage width change amount Y after storage for 10 yearswas obtained from the following equation using the width deformationcoefficient b obtained by the above method.

(Long-term storage width change amount Y after 10-year storage)=blog {10(years)×365 (days)×24 (hours)}

A determination was made on each magnetic tape according to the valuesof the long-term storage width change amount Y (more desirable as thevalues are smaller), and the eight-stage determination values were givento each tape. Note that evaluation “8” indicated the most desirabledetermination result and evaluation “1” indicated the most undesirabledetermination result. The magnetic tape has certain evaluation of the 8stages, and the following states are observed when the magnetic taperuns.

8: No abnormality occurred.

7: A slight increase in error speed is observed when running.

6: A serious increase in error speed is observed when running.

5: During running, the magnetic tape may not read a servo signal andslight (one or two) reloading is performed.

4: During running, the magnetic tape may not read a servo signal andmedium (up to 10 times) reloading is performed.

3: During running, the magnetic tape may not read a servo signal andheavy (more than 10 times) reloading is performed.

2: The magnetic tape may not read servo and occasionally stops due to asystem error.

1: The magnetic tape may not read servo and immediately stops due to asystem error.

Regarding calculation of the width deformation coefficient b and thedetermination after storage for 10 years will be described in furtherdetail using Example 4 as an example.

In the magnetic tape of Example 4, an example of the measurement resultsof the deviation amount (μm) of the servo track width at each positionat which the servo track width deviation amount was measured andcalculation results of the width deformation coefficient b at eachposition are shown in Table 2. As shown in Table 2, in the magnetic tapeof Example 4, a maximum value of the width deformation coefficient b was0.04 μm and a minimum value of the width deformation coefficient b was−0.01 Furthermore, the long-term storage width change amount Y afterstorage for 10 years was obtained using these width deformationcoefficients b, and a determination was made according to the value ofY. As shown in Table 1, a determination of the magnetic tape of Example4 was 6.

(Evaluation of Electromagnetic Conversion Characteristic)

First, a reproduction signal of the magnetic tape was acquired using aloop tester (manufactured by Microphysics). The conditions for acquiringthe reproduction signal are described below.

Head: GMR

Headspeed: 2 m/s

Signal: single recording frequency (10 MHz)

Recording current: Optimal recording current

Next, the reproduction signal was adopted by a spectrum analyzer at aspan (SPAN) of 0 to 20 MHz (resolution band width=100 kHz, VBW=30 kHz).Next, a peak of the adopted spectrum was taken as a signal amount S,floor noise without the peak was integrated to obtain a noise amount N,and a ratio S/N of the signal amount S to the noise amount N wasobtained as a signal-to-noise ratio (SNR). Next, the obtained SNR wasconverted into a relative value (dB) based on the SNR of ComparativeExample 1 as a reference medium. Next, using the SNR (dB) obtained asdescribed above, quality of an electromagnetic conversion characteristicwas determined as follows.

Better: The SNR of the magnetic tape is 1 dB or much better than the SNR(=0(dB)) of the evaluation reference sample (Comparative Example 1).

Good: The SNR of the magnetic tape is equal to or exceeds the SNR(=0(dB) of the evaluation reference sample (Comparative Example 1)

Almost good: There is a portion where the SNR of the magnetic tape isless than the SNR (=0(dB)) of the evaluation reference sample(Comparative Example 1).

Bad: The SNR of the magnetic tape is less than the SNR (=0(dB)) of theevaluation reference sample (Comparative Example 1) over the entirearea.

(Evaluation of Winding Deviation)

First, a magnetic recording cartridge after the above-mentioned“determination of change amount of tape width” was prepared. Next, thereel around which the tape was wound was taken out from the magneticrecording cartridge, and an end face of the wound tape was visuallyobserved. Note that the reel has a flange, and at least one flange istransparent or translucent so that the internal tape winding can beobserved over the flange.

According to results of observation, in a case where the end face of thetape is not flat and there is a step or protrusion of the tape, the tapewas determined to have winding deviation.

Furthermore, the “winding deviation” is considered to be worse as aplurality of steps and protrusions are observed. The above determinationwas made for each sample. The winding deviation state of each sample wascompared with the winding deviation state of Comparative Example 1 as areference medium, and the quality was determined as follows.

Good: In a case where the winding deviation state of the sample is equalto or less than the winding deviation state of the reference sample(comparative example 1).

Bad: In a case where the winding deviation state of the sample is largerthan the winding deviation state of the reference sample (comparativeexample 1).

Table 1 shows the configurations and evaluation results of the magnetictapes of Examples 1 to 25 and Comparative Examples 1 to 4. Furthermore,Table 2 shows an example of the measurement results of the deviationamount (μm) of the servo track width at each position of the magnetictape of Example 4 and the calculation results of the width deformationcoefficient b at each position of the magnetic tape.

TABLE 1 Width Deformation Determi- Coefficient b nation Electro- Maximumafter magnetic Base value/ Storage Conversion Magnetic Thickness t_(T)Δw α β σ_(MD) V t_(m) Alignment S2 t_(b) R_(ab) Minimum for 10Character- Winding Material (μm) [μm] (ppm/N) (ppm/° C.) (ppm/% RH) ρ(N) (mm/min) (nm) Degree [%] (μm) (nm) μ value Years istics DeviationExample 1 ε 3.8 5.5 707 5.9 5.2 0.29 0.75 0.5 90 Substantially 65 0.6 60.50 0.01/−0.01 4 Good Good Iron Vertical Oxide Example 2 ε 3.3 5.0 7505.9 5.2 0.29 0.75 0.5 90 Substantially 65 0.6 6 0.50 0.02/−0.01 5 GoodGood Iron Vertical Oxide Example 3 ε 3.2 4.5 800 5.9 5.2 0.29 0.75 0.590 Substantially 65 0.3 6 0.50 0.04/−0.01 5 Good Good Iron VerticalOxide Example 4 ε 3.2 4.5 800 6 5 0.29 0.75 0.5 90 Substantially 65 0.36 0.50 0.04/−0.01 6 Good Good Iron Vertical Oxide Example 5 ε 3.2 4.5800 8 5 0.29 0.75 0.5 90 Substantially 65 0.3 6 0.50 0.04/−0.01 6 GoodGood Iron Vertical Oxide Example 6 ε 3.2 4.6 800 6 3 0.29 0.75 0.5 90Substantially 65 0.3 6 0.50 0.04/−0.01 7 Good Good Iron Vertical OxideExample 7 ε 3.2 4.5 800 6 5 0.31 0.75 0.5 90 Substantially 65 0.3 6 0.500.04/−0.01 6 Good Good Iron Vertical Oxide Example 8 ε 3.2 4.5 800 6 50.35 0.75 0.5 90 Substantially 65 0.3 6 0.50 0.04/−0.01 6 Good Good IronVertical Oxide Example 9 ε 3.2 4.5 800 6 5 0.31 0.8 0.5 90 Substantially65 0.3 6 0.50 0.04/−0.01 7 Good Good Iron Vertical Oxide Example 10 ε3.2 4.5 800 6 5 0.31 3.5 0.5 90 Substantially 65 0.3 6 0.50 0.04/−0.01 7Good Good Iron Vertical Oxide Example 11 ε 3.2 4.5 800 6 5 0.31 0.8 5 90Substantially 65 0.3 6 0.50 0.04/−0.01 7 Good Good Iron Vertical OxideExample 12 ε 3.2 4.4 800 6 5 0.31 0.75 0.5 40 Substantially 65 0.3 60.50 0.04/−0.01 6 Good Good Iron Vertical Oxide Example 13 CrPtCo 3.64.0 800 6 5 0.31 0.75 0.5 9 Vertical 98 0.3 6 0.50 0.02/−0.01 6 GoodGood SiO2 Example 14 ε 3.2 4.4 800 6 5 0.31 0.75 0.5 90 Substantially 650.2 6 0.50 0.04/−0.01 6 Good Good Iron Vertical Oxide Example 15 ε 3.24.5 800 6 5 0.31 0.75 0.5 90 Substantially 65 0.3 3 0.50 0.04/−0.01 6Good Good Iron Vertical Oxide Example 16 ε 3.2 4.5 800 6 5 0.31 0.75 0.590 Substantially 65 0.3 6 0.20 0.04/−0.01 6 Good Good Iron VerticalOxide Example 17 ε 3.2 4.5 800 6 5 0.31 0.75 0.5 90 Substantially 65 0.33 0.80 0.04/−0.01 6 Good Good Iron Vertical Oxide Example 18 ε 3.2 4.5800 6 5 0.31 0.75 0.5 110 Substantially 65 0.3 6 0.50 0.04/−0.01 6Approx- Good Iron Vertical imately Oxide Good Example 19 ε 3.2 4.5 800 65 0.31 0.75 0.5 90 Substantially 65 0.3 7 0.50 0.04/−0.01 6 Approx- GoodIron Vertical imately Oxide Good Example 20 ε 3.2 4.5 800 6 5 0.31 0.750.5 90 Substantially 65 0.3 6 0.18 0.04/−0.01 6 Good Bad Iron VerticalOxide Example 21 ε 3.2 4.5 800 6 5 0.31 0.75 0.5 90 Substantially 65 0.36 0.82 0.04/−0.01 6 Good Bad Iron Vertical Oxide Example 22 ε 3.2 4.5800 6 5 0.31 0.75 0.5 90 Substantially 73 0.3 6 0.50 0.04/−001 7 GoodGood Iron Vertical Oxide Example 23 ε 3.2 4.5 800 6 5 0.31 0.75 0.5 90Substantially 80 0.3 6 0.50 0.04/−0.01 7 Better Good Iron Vertical OxideExample 24 ε 3.2 4.5 800 6 5 0.31 5.0 0.5 90 Substantially 65 0.3 6 0.500.04/−0.01 7 Good Good Iron Vertical Oxide Example 25 Barium 3.2 4.5 8006 5 0.31 0.75 0.5 90 Substantially 65 0.3 6 0.50 0.04/−0.01 7 Good GoodFerrite Vertical Comparative ε 3.8 5.5 650 5.9 5.2 0.29 0.75 0.5 90Substantially 65 0.6 6 0.50 0.02/−0.01 1 Good Good Example 1 IronVertical Oxide Comparative ε 3.6 5.0 800 5.9 5.2 0.29 0.75 0.5 90Substantially 65 0.3 6 0.50 0.08/−0.02 1 Good Good Example 2 IronVertical Oxide Comparative ε 3.6 5.0 800 5.9 5.2 0.29 0.75 0.5 90Substantially 65 0.3 6 0.50 0.05/−0.09 1 Good Good Example 3 IronVertical Oxide Comparative ε 3.2 4.5 800 6 5 0.29 0.75 0.5 90 Non- 600.3 6 0.50 0.04/−0.01 6 Bad Good Example 4 Iron aligned Oxide

TABLE 2 Width Deformation Storage Time (h) Coefficient 52 100 152 200252 300 b Position (m) of 850 −0.170 −0.155 −0.151 −0.149 −0.144 −0.1380.04 Magnetic Tape 800 −0.189 −0.176 −0.173 −0.175 −0.168 −0.162 0.03 inLongitudinal 750 −0.203 −0.191 −0.187 −0.187 −0.180 −0.177 0.03Direction 700 −0.205 −0.198 −0.201 −0.199 −0.194 −0.189 0.02 650 −0.203−0.196 −0.197 −0.195 −0.192 −0.186 0.02 600 −0.200 −0.192 −0.194 −0.192−0.188 −0.183 0.02 550 −0.200 −0.192 −0.196 −0.194 −0.189 −0.183 0.02500 −0.209 −0.205 −0.208 −0.206 −0.202 −0.195 0.01 450 −0.209 −0.204−0.209 −0.208 −0.204 −0.197 0.01 400 −0.201 −0.199 −0.203 −0.201 −0.200−0.192 0.01 350 −0.201 −0.198 −0.203 −0.201 −0.202 −0.192 0.00 300−0.201 −0.199 −0.205 −0.204 −0.205 −0.196 0.00 250 −0.200 −0.194 −0.204−0.203 −0.203 −0.196 0.00 200 −0.203 −0.199 −0.210 −0.208 −0.210 −0.1990.00 150 −0.204 −0.201 −0.209 −0.212 −0.212 −0.202 −0.01 100 −0.208−0.209 −0.217 −0.220 −0.219 −0.211 −0.01 50 −0.160 −0.142 −0.160 −0.168−0.165 −0.161 −0.01

Note that each symbol in Table 1 refers to the following measurementvalues.

t_(T): Thickness of magnetic tape (unit: μm)

Δw: Dimension change amount in the width direction of the magnetic tapewith respect to a change in tension in the longitudinal direction of themagnetic tape (unit: ppm/N)

α: Thermal expansion coefficient of magnetic tape (unit: ppm/° C.)

β: Humidity expansion coefficient of magnetic tape (unit: ppm/% RH)

ρ: Poisson's ratio of magnetic tape

σ_(MD): Elastic limit value in the longitudinal direction of magnetictape (unit: N)

V: Speed for measuring elastic limit (unit: mm/min)

t_(m): Average thickness of magnetic layer (unit: nm)

S2: Squareness ratio (unit:%) in the thickness direction (verticaldirection) of the magnetic tape (unit: %)

t_(b): Average thickness of back layer (unit: μm)

R_(ab): Surface roughness of back layer (unit: nm)

μ: friction coefficient between magnetic surface and back surface

From the results shown in Table 1, the following can be seen.

In each of the magnetic tapes of Examples 1 to 25, the determinationresults based on the long-term storage width change amount Y afterstorage for 10 years was 4 or more (that is, the value of the long-termstorage width change amount Y is small). Therefore, it can be seen thatthe magnetic recording medium according to the embodiment of the presenttechnology is suitable for use in the recording and reproducingapparatus that adjusts tension in the longitudinal direction, andsuitability thereof for the recording and reproducing apparatus isstably maintained over a long period of time.

From the results of the determination of the change amounts of tapewidths of Examples 1 to 25 and Comparative Example 1, it can be seenthat the dimensional change amount Δw of the magnetic recording tape is660 ppm/N or more, more preferably 700 ppm/N or more, even morepreferably 750 ppm/N, still more preferably 800 ppm/N or more, and thus,the magnetic recording tape is more suitable for use in the recordingand reproducing apparatus for adjusting tension in the longitudinaldirection (in particular, adjustment of the tape width by adjustingtension).

When Example 7 and Comparative Examples 2 and 3 are compared, the widthdeformation coefficient b of the magnetic tape of Example 7 is withinthe range of 0.06 μm≤b≤0.06 μm and the determination result based on thelong-term storage width change amount Y after storage for 10 years is 6,whereas a maximum value of the width deformation coefficient b of themagnetic tape of Comparative Example 2 exceeds 0.06 μm and thedetermination result based on the long-term storage width change amountY after storage for 10 years was 1. Furthermore, in the magnetic tape ofComparative Example 3, the minimum value of the width deformationcoefficient b was less than −0.06 μm and the determination result basedon the long-term storage width change amount Y after storage for 10years was 1. Therefore, it can be seen that suitability of the magneticrecording tape to the recording and reproducing apparatus is stablymaintained over a long period of time when the width deformationcoefficient b is within the range of −0.06 μm≤b≤0.06 μm.

From the comparison of the evaluation results of Examples 3 to 6 and thelike, it can be seen that it is preferable that the temperatureexpansion coefficient α is 5.9 ppm/° C.≤α≤8 ppm/° C. from the viewpointof decreasing the value of the long-term storage width change amount Y.From the comparison of the evaluation results of Examples 3 to 6 and thelike, it can be seen that it is preferable that the humidity expansioncoefficient β is β≤5 ppm/% RH from the viewpoint of decreasing the valueof the long-term storage width change amount Y.

From the comparison of the evaluation results of Examples 7, 9, and 10,it can be seen that it is preferable that the elastic limit value σ_(MD)in the longitudinal direction is 0.8 N≤σ_(MD) from the viewpoint ofdecreasing the value of the long-term storage width change amount Y.

From the comparison of Examples 9 and 11, it can be seen that theelastic limit value σ_(MD) does not depend on the speed V when theelastic limit measurement is performed.

From the comparison of the evaluation results of Examples 7 and 18, itcan be seen that the thickness of the magnetic layer is preferably 100nm or less, particularly 90 nm or less, from the viewpoint of improvingelectromagnetic conversion characteristic.

From the comparison of the evaluation results of Examples 7, 15, 17 and19, it can be seen that the surface roughness R_(ab) of the back layeris preferably 3.0 nm≤R_(ab)≤7.5 nm from the viewpoint of improvingelectromagnetic conversion characteristic.

When the evaluation results of Examples 7, 16, 17, 20, and 21 arecompared with each other, the friction coefficient μ is 0.18<μ<0.82,particularly 0.20≤μ≤0.80, more particularly, 0.20≤μ≤0.78, and still moreparticularly, 0.25≤μ≤0.75, from the viewpoint of suppressing windingdeviation.

When Example 7 and Comparative Example 4 are compared with each other,it is preferable that the magnetic layer is aligned vertically orsubstantially vertically, from the viewpoint of improving theelectromagnetic conversion characteristic. Furthermore, from thecomparison of the evaluation results of Examples 7, 22, and 23, it canbe seen that the squareness ratio S2 of the magnetic tape in thevertical direction is preferably 73% or more, and particularly 80% ormore, from the viewpoint of improving electromagnetic conversioncharacteristic.

From the comparison of the evaluation results of Examples 7, 25 and thelike, it can be seen that evaluation results similar to those obtainedusing ε iron oxide nanoparticles as magnetic particles can be obtainedeven in a case where the barium ferrite nanoparticles are used asmagnetic particles.

From the comparison of the results of Example 13 and other Examples, itcan be seen that evaluation results similar to those of the coating typemagnetic recording tape can be obtained even with the vacuum thin filmtype (sputter type) magnetic recording tape is used.

Although the embodiments and examples of the present technology havebeen specifically described above, the present technology is not limitedto the above-described embodiments and examples, and variousmodifications may be made on the basis of the technical idea of thepresent technology.

For example, the configurations, methods, steps, shapes, materials, andnumerical values or the like in the above embodiments and examples aremerely examples, and a configuration, a method, a step, a shape, amaterial and a numerical value or the like different therefrom may alsobe used. Furthermore, the chemical formulas of the compounds and thelike are typical, and are not limited to the mentioned valences in caseof the generic name of the same compound.

Furthermore, the configurations, methods, steps, shapes, materials, andnumerical values or the like of the above-described embodiments andexamples may be combined without departing from the spirit of thepresent technology.

Furthermore, in this specification, the numerical value range indicatedby “to” indicates the range including the numerical values mentionedbefore and after “to” as the minimum value and the maximum value,respectively. In the numerical range mentioned stepwise in thisspecification, the upper or lower limit of the numerical range of acertain stage may be replaced with the upper or lower limit of thenumerical range of the other stage. The materials exemplified in thisspecification can be used alone or in combination of two or more, unlessotherwise specified.

Note that the present technology can have the following configuration.

[1] A magnetic recording medium of which

an average thickness t_(T) is t_(T)≤5.6 μm,

a dimensional change amount Δw in a width direction with respect to achange in tension in a longitudinal direction is 660 ppm/N≤Δw,

a squareness ratio in a vertical direction is 65% or more, and

a width deformation coefficient b during long-term storage in a casewhere a long-term storage width change amount Y is defined as Y=blog(t)is −0.06 μm≤b≤0.06 μm.

[2] The magnetic recording medium described in [1], in which themagnetic recording medium is used in a timing servo type magneticrecording and reproducing apparatus.

[3] The magnetic recording medium described in [1] or [2], in which thedimensional change amount Δw is 700 ppm/N≤Δw.

[4] The magnetic recording medium described in [1] or [2], in which thedimensional change amount Δw is 750 ppm/N≤Δw.

[5] The magnetic recording medium described in [1] or [2], in which thedimensional change amount Δw is 800 ppm/N≤Δw.

[6] The magnetic recording medium described in any one of [1] to [5],

in which the magnetic recording medium includes a back layer, and

a surface roughness R_(ab) of the back layer is 3.0 nm≤R_(ab)≤7.5 nm.

[7] The magnetic recording medium described in any one of [1] to [6],

in which the magnetic recording medium includes a magnetic layer and aback layer, and

a friction coefficient μ between a surface on a side of the magneticlayer and a surface on a side of the back layer is 0.20≤μ≤0.80.

[8] The magnetic recording medium described in any one of [1] to [7], inwhich a temperature expansion coefficient α is 5.5 ppm/° C.≤α≤9 ppm/°C., and a humidity expansion coefficient β is β≤5.5 ppm/% RH.

[9] The magnetic recording medium described in any one of [1] to [8] inwhich Poisson's ratio ρ is 0.25≤ρ.

[10] The magnetic recording medium described in any one of [1] to [9],in which an elastic limit value σ_(MD) in the longitudinal direction is0.7 N≤σ_(MD).

[11] The magnetic recording medium described in [10], in which theelastic limit value σ_(MD) does not depend on a speed V at a time ofmeasuring an elastic limit.

[12] The magnetic recording medium described in any one of [1] to [11],

in which the magnetic recording medium includes a magnetic layer, and

the magnetic layer is vertically aligned.

[13] The magnetic recording medium described in any one of [1] to [12],

in which the magnetic recording medium includes a back layer, and

an average thickness t_(b) is t_(b)≤0.6 μm.

[14] The magnetic recording medium described in any one of [1] to [13],

in which the magnetic recording medium includes a magnetic layer, and

the magnetic layer is a sputtered layer.

[15] The magnetic recording medium described in [14], in which anaverage thickness t_(m) is 9 nm≤t_(m)≤90 nm.

[16] The magnetic recording medium described in any one of [1] to [13],

in which the magnetic recording medium includes a magnetic layer, and

the magnetic layer contains magnetic powder.

[17] The magnetic recording medium described in [16], in which anaverage thickness t_(m) is 35 nm≤t_(m)≤120 nm.

[18] The magnetic recording medium described in [16] or [17], in whichthe magnetic powder contains ε iron oxide magnetic powder, bariumferrite magnetic powder, cobalt ferrite magnetic powder, or strontiumferrite magnetic powder.

REFERENCE SIGNS LIST

10 Magnetic recording medium

11 Base layer

12 Ground layer

13 Magnetic layer

14 Back layer

1. A magnetic recording medium comprising: a magnetic layer, anon-magnetic layer, a base layer, and a back layer, wherein an averagethickness t_(T) of the magnetic recording medium is t_(T)≤5.3 μm, adimensional change amount Δw in a width direction with respect to achange in tension in a longitudinal direction is 700 ppm/N≤Δw, athickness of the non-magnetic layer is 2.0 μm or less, a squarenessratio measured in a vertical direction of the magnetic recording mediumis 65% or more, a width deformation coefficient b during long-termstorage in a case where a long-term storage width change amount Y isdefined as Y=blog(t) is −0.06≤b≤0.06, and the magnetic layer includes amagnetic powder.
 2. The magnetic recording medium according to claim 1,wherein the dimensional change amount Δw is 710 ppm/N≤Δw.
 3. Themagnetic recording medium according to claim 1, wherein the dimensionalchange amount Δw is 730 ppm/N≤Δw.
 4. The magnetic recording mediumaccording to claim 1, wherein the dimensional change amount Δw is 750ppm/N≤Δw.
 5. The magnetic recording medium according to claim 1, whereina thermal expansion coefficient α of the magnetic recording medium is5.5 ppm/° C.≤α≤9 ppm/° C.
 6. The magnetic recording medium according toclaim 1, wherein a thermal expansion coefficient α of the magneticrecording medium is 5.9 ppm/° C.≤α≤9 ppm/° C.
 7. The magnetic recordingmedium according to claim 1, wherein a humidity expansion coefficient βof the magnetic recording medium is β≤5.5 ppm/% RH.
 8. The magneticrecording medium according to claim 1, wherein a humidity expansioncoefficient β of the magnetic recording medium is β≤5.2 ppm/% RH.
 9. Themagnetic recording medium according to claim 1, wherein a humidityexpansion coefficient β of the magnetic recording medium is β≤5.0 ppm/%RH.
 10. The magnetic recording medium according to claim 1, wherein aPoisson's ratio ρ of the magnetic recording medium is 0.25≤ρ.
 11. Themagnetic recording medium according to claim 1, wherein a Poisson'sratio ρ of the magnetic recording medium is 0.29≤ρ.
 12. The magneticrecording medium according to claim 1, wherein a Poisson's ratio ρ ofthe magnetic recording medium is 0.3≤ρ.
 13. The magnetic recordingmedium according to claim 1, wherein an elastic limit value σ_(MD) ofthe magnetic recording medium 0.7 N≤σ_(MD).
 14. The magnetic recordingmedium according to claim 1, wherein an elastic limit value σ_(MD) ofthe magnetic recording medium 0.75 N≤σ_(MD).
 15. The magnetic recordingmedium according to claim 1, wherein an elastic limit value σ_(MD) ofthe magnetic recording medium 0.8 N≤σ_(MD).
 16. The magnetic recordingmedium according to claim 1, wherein the average thickness t_(T) of themagnetic recording medium is t_(T)≤5.2 μm.
 17. The magnetic recordingmedium according to claim 1, wherein the average thickness t_(T) of themagnetic recording medium is t_(T)≤5.0 μm.
 18. The magnetic recordingmedium according to claim 1, wherein the average thickness t_(T) of themagnetic recording medium is t_(T)≤4.6 μm.
 19. The magnetic recordingmedium according to claim 1, wherein the thickness of the non-magneticlayer is 1.4 μm or less.
 20. The magnetic recording medium according toclaim 1, wherein the thickness of the non-magnetic layer is 0.6 μm ormore.
 21. The magnetic recording medium according to claim 1, whereinthe thickness of the non-magnetic layer is 0.8 μm or more.
 22. Themagnetic recording medium according to claim 1, wherein the magneticpowder includes ε iron oxide magnetic powder, barium ferrite magneticpowder, cobalt ferrite magnetic powder, or strontium ferrite magneticpowder.
 23. The magnetic recording medium according to claim 1, whereinthe dimensional change amount Δw is determined by substituting D(0.2 N)and D(1.0 N) for a following equation wherein D(0.2 N) and D(1.0 N)represent widths of a ½ inch-wide magnetic recording medium which is cutinto a length of 250 mm when 0.2 N and 1.0 N are loaded in thelongitudinal direction of the ½ inch-wide magnetic recording medium,respectively:${\Delta \; {w\left\lbrack {{ppm}/N} \right\rbrack}} = {\frac{{{D\left( {0.2N} \right)}\lbrack{mm}\rbrack} - {{D\left( {1.0N} \right)}\lbrack{mm}\rbrack}}{{D\left( {0.2N} \right)}\lbrack{mm}\rbrack} \times {\frac{1,000,000}{\left( {1.0\lbrack N\rbrack} \right) - \left( {0.2\lbrack N\rbrack} \right)}.}}$24. The magnetic recording medium according to claim 1, wherein themagnetic recording medium is used in a timing servo type magneticrecording and reproducing apparatus.
 25. The magnetic recording mediumaccording to claim 1, wherein a surface roughness R_(ab) of the backlayer is 3.0 nm≤R_(ab)≤7.5 nm.
 26. The magnetic recording mediumaccording to claim 1, wherein a friction coefficient μ between a surfaceon a side of the magnetic layer and a surface on a side of the backlayer is 0.20≤μ≤0.80.
 27. The magnetic recording medium according toclaim 1, wherein the magnetic layer is vertically aligned.
 28. Themagnetic recording medium according to claim 1, wherein an averagethickness tb of the back layer is tb≤0.6 μm.
 29. The magnetic recordingmedium according to claim 1, wherein an average thickness tm of themagnetic layer is 35 nm≤tm≤120 nm.
 30. A magnetic recording cartridgecomprising: a cartridge case; a cartridge reel which is accommodated inthe cartridge case; and a magnetic recording medium which is woundaround the cartridge reel, the magnetic recording medium including amagnetic layer, a non-magnetic layer, a base layer, and a back layer;wherein an average thickness t_(T) of the magnetic recording medium ist_(T)≤5.3 μm, a dimensional change amount Δw in a width direction withrespect to a change in tension in a longitudinal direction is 700ppm/N≤Δw, a thickness of the non-magnetic layer is 2.0 μm or less, asquareness ratio measured in a vertical direction of the magneticrecording medium is 65% or more, a width deformation coefficient bduring long-term storage in a case where a long-term storage widthchange amount Y is defined as Y=blog(t) is −0.06≤b≤0.06, and themagnetic layer has a magnetic powder.
 31. The magnetic recording mediumaccording to claim 1, further comprising a barrier layer providedbetween the base layer and the back layer, wherein the barrier layerincludes a metal or metal oxide.
 32. The magnetic recording cartridgeaccording to claim 30, wherein the magnetic recording medium includes abarrier layer provided between the base layer and the back layer, andwherein the barrier layer includes a metal or metal oxide.
 33. Themagnetic recording medium according to claim 1, wherein the squarenessratio ranges from 80% or more.
 34. The magnetic recording cartridgeaccording to claim 30, wherein the squareness ratio ranges from 80% ormore.
 35. The magnetic recording medium according to claim 1, whereinthe dimensional change amount Δw is 700 ppm/N≤Δw≤800 ppm/N.
 36. Themagnetic recording cartridge according to claim 30, wherein thedimensional change amount Δw is 700 ppm/N≤Δw≤800 ppm/N.
 37. The magneticrecording medium according to claim 1, wherein the width deformationcoefficient b is −0.01≤b≤0.04.
 38. The magnetic recording cartridgeaccording to claim 30, wherein the width deformation coefficient b is−0.01≤b≤0.04.